Thanks for the info and the links!!
Today I picked up an airtight container that will hold 38 cups. (It's a Lock&Lock, so there's a nice tight seal.)
Next week we'll be getting our dedicated veggie fridge. Luckily, we got the kind that has the separate freezer section, and I think the container I got today will fit into the freezer section. (I hope!) (It's just a little compact dorm fridge, but 3.1 cubic feet will get all the rabbit food out of the kitchen refrigerator.)
I'm going to wash and dry the container, then fill it with pellets and freeze it right away. Switch it to the veggie fridge next week. I think that should hold half the bag of pellets, so hopefully I won't end up throwing any away.
Next time, I will probably get the 25lb bag instead! lol.