additionally, you can then go into the 'keylist.txt', scroll all the way to the bottom where it says '#Floating icon keys:'.
you'll see a series of numbers that correspond to (for example) potions you've just assigned to function keys (example: 8137 - f8 means small health potion = f8). where the function key you've just assigned is listed, you can now change that to any unused letter (say 'h' for health = 8137 - h).
click 'file/save' and close. now hitting the 'h' key will drink a small health potion.
a couple things of note - firstly; the designated key will cause the LEAD character only to drink the potion (in this case, a small health). you'll still need to switch between characters.
secondly; you'll see your saved hotkey as a CAPITAL letter (example: 8137 - H -), but you need to type it in and save it as a lower case - h. it's converts to a capital once you've started the game.