If you plan on lots of seed collecting and trading, there are several good, commercially available
containers, including small, clear plastic zip bags (craft stores, hardware stores, electronic parts stores); paper coin envelopes
(stationery and office supply stores); and glassine envelopes (stamp and coin collecting suppliers, some craft and art stores).
There are advantages and disadvantages to each of these. Plastic bags allow easy viewing of the seeds
but offer no protection from light and will absorb any available heat. They close securely and are moisture proof but will
retain moisture if seeds aren't dried adequately (a few grains of dry rice with the seeds helps prevent mildew); they are
slippery to handle and difficult to write on; and they offer little cushioning to the seeds they contain.
Paper coin envelopes close securely but cannot be opened and reclosed easily and may 'leak' small seeds
at the corners (tape all corners to prevent this). They are light proof; allow for a certain amount of air circulation but
are not moisture proof; are easy to label, write on and handle; and offer some cushioning to seeds.
Glassine envelopes are barely adequate by themselves (tear very easily, etc.) but are good containers
for very small seeds when used in combination with an outer envelope.