I thought I would share my method of packing and shipping seedlings. I have shipped several Nepenthes and Drosera seedlings recently, using this method.
1. Bareroot the seedlings.
2. Put them in a small, rigid, plastic container, carefully placed between strands of long-fiber sphagnum.
3. Cap container(s) and put inside of a plastic bag.
4. Place inside of a big, yellow, bubblewrap-lined envelope.
5. Seal and address envelope. Hint: Better-looking envelopes and packages get treated better in the mail system.
6. Bring the envelope to the Post Office. You will be charged about $1.51 (3oz) or $1.64 (4 oz). Alternatively, you could weigh the envelope at home, find the postage rates online, put the needed number of stamps on the envelope, and drop it in a mailing bin.