Never. very rarely share a stage with another band but when we have, I always use my gear, it's always better than other bass setups, IMO. Being left handed means lending my bass is a no, no as well. Our drummer uses a double kit so unless there is a double pedal around, he uses his own kit and the way he sets it up means most drummers can't play his anyway.
If we were playing with another band and their gear broke, then I'd be the first one to offer help. but don't expect to use to use mine, it won't happen. Same with the P.A.