zip freezer bags for storing film in the fridge. But now that I've read about there use for 4x5 film holders I'm going to be all over that, thanks guys!
Cotton Swabs (Q-tips) and alcohol for cleaning.
And not quite household, but gaffer tape has been an incredible help in too many ways to mention them all, but here's a few: I've used to to seal light leaks, for temporary repair of cameras while out and about, for insuring my Holga doesn't suddenly open with film in it, for labeling a camera with what film is within (Use a light colored tape for that), holding up a sheet paper as a background. I always have some with me when I'm out shooting. If I'm traveling light, which is most often, I'll take some from the spool and wind it around a 35mm film canister and shove it in my bag.