Which of these skills would be most useful to me as a bassist and which would I never get hired for?

Vocals?

Slap?

Fretless?

Walking?

Soloing?

Playing with a pick?

Tuba?

Cello?

Guitar?

Piano?

Drums?

I can already play BG, DB (pizz and arco), read music and make up parts on the fly. However, there are some areas where my skill is lousy or nonexistent, or some areas where I have some experience but I'd need to buy gear (fretless or guitar). I'm not sure how much I need them for weddings, banquets etc., though.

Vocals.
Keyboard.

too many guitarists in the world. One skill that I wouldn't spend a lot of time on unless you feel it.

I have never gotten hired to solo, but you need to be able to solo, cause you will get some and don't wanna look silly.

Agree with BassChuck
Vocals will help you get and keep gigs. Keys will make you a better musician/player.
If you can't walk over changes, you DEFINITELY need that skill for a lot of different kinds of gigs.
Slap is helpful depending on the gig.

Which of these skills would be most useful to me as a bassist and which would I never get hired for?

Vocals? --- The most important skill by far. It's gotten me several gigs I wouldn't have gotten otherwise.

Slap? --- Good to know, not as necessary as it once was.

Fretless? --- I've only been asked once to play fretless in 30 years. It doesn't hurt to know how to play one, but it won't make or break you.

Walking? --- Absolutely!

Soloing? --- You don't need to know how to solo until someone turns to you and says, "Take it!" Maybe it will happen, maybe it won't. Depends on the music you play. If you play jazz, definitely. All other types of music are a crapshoot.

Playing with a pick? --- I think yes, others think it's an insult to ever be asked to play with a pick. But my pick playing has got me gigs, especially in harder rock bands when I was younger.

Tuba? --- Nah.

Cello? --- Nah.

Guitar? --- Nah, but I do enjoy playing guitar now and then.

Piano? --- I think every musician should at least know enough piano to use it to arrange. You don't have to be good at it, but you need to know what the notes are and be able to form chords.

Drums? --- Some say no, I say absolutely. I started on drums, so I came into bass already knowing how to play drums, and it greatly helped with things like understanding how bass can work with drums (or against them).

I think all of these are useful. Think of it this way...you'd never really have to hire musicians to record if you play all your own instruments. You'd have to hire them to go on tour.

Thanks, everyone. So far it's like I'd have guessed - vocals, piano and walking are the most useful in the real world. I do have some basic skill at all three but need to improve it and buy at least a cheap keyboard. Drums are tempting.

I think all of these are useful. Think of it this way...you'd never really have to hire musicians to record if you play all your own instruments. You'd have to hire them to go on tour.

True, but for my own metal bands I already have all the needed skills and equipment except drums and maybe banjo. Drums are a maybe as well, on a couple songs I recently did I used my DB for percussion... just smacked the body with my hands.

IME:

Useful - Vocals, reading (chord charts and notation), picking up parts by ear, traditional P or J tone, solid pick and fingerstyle technique, vocals, professional quality amplification, ability to compose basslines (but not songs!), good relationship (both musical and personal) with drummer, eye contact with bandmembers, ability and willingness to move heavy equipment and help others set up, vocals, and general people skills.

Slap and tap may be useful depending on the gig, but 80% of the gigs I've taken don't require either. It goes without saying that walking is essential for jazz gigs, but most pop and rock bands absolutely hate it.

Useless - Fretless, more than 5 strings, soloing, and any other instruments except double bass and perhaps keyboards.

If you have time, of course, learn to do everything, but don't expect to use all of your skills if you get hired as "just the bassplayer."

Vocals.
Keyboard.
+1


Vocals?
Probably the most important. I have seen bassist with mediocre skills get great jobs because they can sing.
Slap?
More or less depending on the style of music. Still a good technique to have for two reasons. 1. It's good to know if a job comes up that requires it, rather than trying to learn on the job. 2. Knowing the technique (or any other mater of fact) will make you approach a bass line differently if it's used or not.
Fretless?
Another one more or less depending on the style of music, but better to have than not if a job comes along.
Walking?
Definitely in my book. It's mostly in blues and jazz, but mostly for one reason. Learn to swing!! (and shuffle). Knowing how to apply a swing or shuffle feel to different types of music is important. Listen to Motown and you'll get what I mean.

Soloing?
I'm a mediocre soloist and I wish I could do a better job. More than likely you will get the call to do one so it's a good idea to have some chops.

Playing with a pick?
Good skill to have if you are doing covers where there may be a lot of tunes with pick players. I've been playing for about twenty five years and have been able to avoid it.

Tuba? Cello? Guitar? Piano? Drums?
I think learning any other instrument other than your main instrument is a good thing. It will make you approach your bass playing differently. You just have to determine which will be best for you because it will take time away from playing the bass. Which one do you think you may use the most or benefit from the most.

I find the most important and effective is being able to add vocals and an ear for harmony. It adds another part to the music and makes you more of an asset to the whole package. Next would be walking or just plain being to hold down a good steady bass line, add a little color where appropriate but doesn't have to be anything fancy, just solid. I usually don't play with a pick but always have a couple along just in case that sound is a necessary part of some song you end up playing. Chunk-O-Funk's line about learning slap even if you don't use to make you think differently about the bass line also applies to owning at least some sort of 5-string bass even a cheap one to play at home. Even if you never play anything that requires a low B string, just having it there will make you look at the fretboard differently and open up your usual playing.

sight reading, doubling on upright and singing are the three things that will set you apart from the crowd.

imho

If purchasing and learning tuba/soussaphone is something that you could pull off, and you want to make a living playing all kinds of music, I'd say absolutely. I've read that at the turn of the century, most bassists doubled on string bass and "brass bass", and would bring whatever was most suitable for the gig, just like a lot of guys play electric and upright today. There's still a few guys who double on both in New Orleans.

EDIT: And I would put walking and soloing way above anything else.

pklima - it all depends upon the types of gigs you are going to do. It's true that vocals are almost always appreciated and I'd say that slapping is useful (but not always necessary). You really should know how to do walking bass lines - I would guess that you'll lose gigs if you don't have a feel for that.

The gigs I'm after are paid ones, preferably well-paid. Other than that I have few restrictions. I refuse to play patriotic music from foreign countries (other than Poland and Texas) or the songs of enemy sports clubs. I don't like to play music that mostly musicians like.

I've been asked if I can sing a lot. I've been asked if I play cello a few times. I've been asked if I play tuba exactly as often as I've been asked to slap - once. Though if I ever ended up a miner, railroad worker, fireman or soldier I'd probably have to learn tuba - those groups make up most of Poland's brass bands. It might be useful for playing dances for older crowds (lots of polkas, waltzes etc.) but rarely necessary.