Adjust and tighten the headset(s) properly before your trip. Use grease and get the nuts well tightened against each other. You shouldn't have a problem. In the unlikely event it loosens up on you, you can stop at any auto mechanic shop and ask to borrow a wrench, channel locks, whatever to get you to the next bike shop. It takes some trial and error, but it can be done with one wrench on just the top nut.

I wouldn't carry any headset tools on a tour -- too heavy and bulky, and most likely unnecessary.