Leftover pizza slices - handy to have on hand for lunch when you don't feel like a sandwich, or pop a slice in your children's lunchboxes
butter - as a bake-a-holic I like to keep a packet of butter in the freezer so I'm never too far from a homemade cake!
tomato paste - if I put leftover tomato paste in the fridge it's always forgotten and goes mouldy, so now I keep it in the freezer
ginger - did you know you can freeze ginger? Simply cut it into chunks and store in a ziplock bag then you can pull out a piece when you need it. And it's easier to peel and chop/grate the ginger while it's frozen.
leftover wine - I don't know if you have any leftover wine at your place, but if you do then pour it into a ziplock bag and freeze it until you need wine in a recipe
cooked rice - I like to fill the rice cooker to the max then I'll bag up the leftover rice and freeze it for another meal
egg whites - whenever I use egg yolks I keep the white in the freezer and stockpile them until I have enough for a pavlova
Hope that helps. Post a comment below if you have any questions.