Anything but money unless you can have a conversation with them and no alarms go off.
Food/water is a good way to test the waters and makes sense to be a first resort. Offer to fill up their car (within MPG boundaries to their stated destination +/- 10 miles) if it's gas, don't give cash and if that's all you have then go inside and put it on the pump they are on. If they are standing around with a can, offer to fill it up for them personally. I wouldn't expect anyone to blindly trust me and if that were their only condition for helping me out with gas...why would anyone have an issue?
True it is possible after the nightmare of a day they "may" have had that a lack of trust could be the last straw but pretty unlikely.
I love to help people, but you do have to set limits and be wary. If they can't respect your boundaries, it's not a good sign.
I could type a long post on this one with all the random experiences I've had. Each one has held a lesson of some kind. It's pretty neat, perhaps I'll share a little bit when I don't have to stand to type :s
I've learned lots and really it's the people that don't ask that you should be on the lookout for. Would you ask? Most here the first time they are in that situation would find that uncomfortable and would just be praying that God sends some help to them. Maybe sometimes YOU are that help? I've had experiences of helping and being helped. It is uncomfortable to ask though if someone is alright or needs anything randomly but almost every time I have, they do.
Ach. There's so much to say but I'll leave it here for a bit. Listen to the Lord and be mindful of feeling "guilty" or "pressured". You should feel peace in your spirit in my experience.
Perhaps a Part 2