Couldn't agree more Yasha Hime,
If you train hard at the dojang, then do just a little work everyday at home, then you'll get a lot more out of Tae Kwon Do. You don't need to do much at home, just run through the patternsa couple of times everyday, which takes maybe 2 minutes, and you'll remember them better.
Personally I can spend half an hour going through one pattern, because it helps me to understand the movements of the rest of tae kwon do.
I would also advise just doing some general fitness stuff. Tae Kwon Do is basically a power sport, so do some sprinting. You can do a bit of long distance running, but I would focus more on recovery times. Don't buy ankle weights, infact don't buy anything you don't absolutely need. I have a pair of good running shoes and access to my school's gym, and that's all I need.