For the large stuff If you can ship it yourself when you are in the USA, to your own address in the UK that is on your id, not only will you get your sales tax back but you won't need to carry things back yourself. Also, many places only list price minus sales tax, you only find out that the thing for $125 costs $250 at the till.
Otherwise the GBP/USD rate is stacked up against the buy-in-US at the moment. Hopefully that improves into the year.
Ship it via some cheap surface transport - and it gets here in 2 weeks. And delivered to your door.
The key is to be the person who ships it, and be the person recieving it, at your permanent address.
Otherwise, some amazing shops and very good prices to be had for kit in places like REI etc and a bunch of stuff like ram mounts, emergency kit + recovery kit, radios. Just keep in mind that not everything there is free voltage,.like we have gotten used to.
Since you have a hundy, you can find loads of things for it too.
And if you are ever in Salt Lake area remember the land cruiser museum..
Many areas have 4x4 clubs and every single one I have approached ahead of time has been welcoming to their meetups, and there are some large events worth going to like the Overland Expo's.
What else ? I guess if you are there often enough get a credit card with very good security, and someone who won't charge for exchange.
Other than that, I guess enjoy the diversity of the US!