I store my seeds in their original envelopes in a surplus ammo box. The
thing has a rubber gasket in the lid which keeps moisture out and the
box takes abuse like nothing else I can think of. I made a tray for the
top to hold bags of silica gel (for keeping it dry inside). Some of the
envelopes come with reusable stickum, but if not I use magic tape or
other resealable tape. When I plant out a flat I put the envelopes for
the seeds I used together in a separate envelope and label with the date
planted: that way, if any of the seeds shows poor germination I know
where to find it to get rid of. (It's also info backup if the flat
marker gets lost or unreadable.)