Hard to pick a favorite so I'll list several:
My 500gb WD "my passport" HD
wireless thermometer from bass pro shop (for reading outside air temps)

and all the grill stuff from my GF:
Weber basting brush/bowl
Weber 'kabob set
Hasty Bake solid wood grill brush (had a dif. kind that broke before)
a griddle for my grill
a grill wok
beer can holder for grilling beer can chicken (helps keep the thing from fallin' over)
2 weber 'oven' mits for the grill

-David