No problem/All right/Of course/You got it/Happy to help/Whatever you want(need)/All you have to do is ask.
That depends/I don't think I can/I'd rather not/I don't think so/Sorry, I can't/Not this time/You are asking for too much/Forget it/No way.
A: Would you mind taking care of my plants while I'm out of town?
B: Whatever you need, just tell me what I need to do.
A: Hey, would you mind closing the door?
B: Sure, no problem.
A: Could you save my seat while I run and get some snacks?
B: That depends. Can you bring me back something too?