Check out my seedling pot instructable. This one shows how to collect and store the tubes until time to make pots.
Step 1: Step 35
Simple locate a coin box. I acquired mine from the bank, we did a gag gift worth $25 in pennies. Interestingly enough, the box holds toilet paper tubes perfectly. I ripped the flaps off of the box, simply for ease of use.
Simply flatten them and stack in the box.
Once you've collected enough, you can make a whole bunch of seedling pots.