In my experience, there are some useful bit's of US military surplus kit that seem to be hard to find or expensive over here in UK. If you can get some of the following, i dont think you'll go far wrong.
1. US quilted poncho/sleeping bag liner. Usually in woodland camo, it is a fantastic warm weather quilt or hammock accessory. Very light and fold/roll up to nothing.
2. Old US cinch back hide combat gloves. Tough as you like, last forever, ideal for camp work.
3. BDU trousers in any colour /cam that take your fancy. Heavy weight or light weight versions, you can pick them up for pennies out there and they are durable as well as cheap.
4. Paracord. It seem's readily available in MANYdifferent colours and thickness's at a fraction of the price over here.
5. Boots. Danner boots and Matterhorn boots are available over here but with a serious mark up in price. Over there you have more choice of styles, more choice in size and you'll be paying 1/3 of the price compared to over here.
Just a few suggestions, make of them what you will but i did'nt miss the chance when i went over there and have not regretted it ever since. Every time i go out, people ask me how much i paid for my brown Danners and where i got them from. The look on their faces when i works out that i paid less for them than a pair of Hi-Tec's over here!
Just watch out for import duty. If you try to import over £32 worth of items (i think) into this country, your liable for duty. But if you've worn the boots, they are no longer new! Anyway, it's up to them to prove you did not take the kit out with you in the first place!
Good luck and enjoy the trip!