I've had the same fishing buddy for 12 years and we just alternate driving trips. We always split the costs of everything 50/50(over the years it always evens out). If I see a fly that might work better, i buy at least 2 and vice versa with him. We've gone with others on trips and it is a pistol to watch them count pennies and yes run to the potty when it's time to gas up. It has even gotten to where one of us makes the sandwiches for an outing and the other picks up the snack and stuff. We take at least one "big" trip a year( same 50/50 split) and usually go out 2-3 times a month (in AZ it's all year round).

Set up the expectations up front and hold to them..Heck..even our wives remind us whose turn it is to drive or who makes lunch and they don't go fishing with us!

We find it is fun to take a kid along (10-teen) and get them involved we expect nothing from them..
Get new friends!!!!