Walking out on gigs is never a good idea unless it's something MAJOR. Seriously, that's a good way to not get hired by groups. I fired a guitarist for that once. Just don't do it. I know the situation sucked, trust me, I've been there, but don't walk out on gigs. The only one who loses is you.
Second, get your own monitor , an ear monitor or a wedge, it never hurts to have your own personal gear. I ALWAYS bring: A mic for my cab, some form of monitor, and some form of tuner. ALWAYS even if I'm using my amp as a DI, I still bring a mic for my cab. Why? Because you never know. Plan ahead. NEVER reply on other people for gear. When I played drums I brought my own set of drum mics whether I needed them or not. JUST IN CASE. Hell I bring my own guitar stands and even extra cables, as well as a tool kit. I've got the gear to do a basic set-up on a bass or guitar if need be. Remember the Boy scout motto: Be prepared!