That's tough man, about you're dad. My 'rents have been reasonably healthy so far, but you know the day is coming ....
Anyway, I find that the "small electronics" are good buys whenever I hit the States. Pedals tend to be cheaper there, are easily portable, and there aren't usually any electricity issues :).
IMO a wah is the most important guitar pedal, but you've sorted your wah situation :). A lot of people like an overdrive/distortion pedal (to kick in a little boost on solos), though you'll have to try different stuff to see what suits your ears. Zakk used a Boss SD-1, now has his own MXR signature pedal. I like the tube screamer type pedals; the stock OD-9 Maxon seemed pretty good when I tried it, though my budget isn't ready for more pedals right now!
You could go totally nuts buying pedals, which is fun, but you would probably end up changing your mind later about what you really liked. But I'd say that, along with a wah and an overdrive, a delay pedal is useful; a lotta people go with a chorus pedal and a compressor as well. Oh, don't neglect a tuner! I swear that my Boss TU-2 is the most useful guitar/bass accessory I've ever bought :)
Getting away from pure guitar gear, the other most significant saving I made on a US purchase was on my USB audio interface (a Tascam US-122). It's small and portable and runs off my computer's power, and was markedly cheaper in the US than in the UK. This is the most important piece of kit I bought in the last year, since it lets be run microphones or direct right into my computer for recording purposes. Even if you buy a whole new computer in the UK, consider picking up your audio interface in the US! Sometimes (but not always) microphones are cheaper in the US (depends on the make). Use the web to check US and UK prices.
