I was just wondering about this! Going to be traveling (flying) in a couple weeks and want to take some kefir grains (which I've been using to kefir coconut milk) to share with my mom. I have packed all sorts of food before, checked, carry-on etc. Don't expect to take anything in your carry-on unless it is dry/solid and I wouldn't take anything that looks 'suspicious' or has any type of cultures involved. The word 'bacteria' would send the airports into a tizzy I imagine. I had to chuckle a while back because the media was just ripping apart someone whose honey (in his checked luggage) held up a flight because it aroused suspicion. I've DEFINITELY traveled with honey before (checked)--hey--I'm not going to leave a half-finished jar of organic raw honey behind after buying it on vacation! Ah...the things TF makes us do ;-)
Anyway, maybe just take SOME of your grains, checked, in some liquid that will support them but not SO nutritive that they'll grow like crazy and create gas that will pop open their container. I'd put it in something with a screw top, preferably leak-proof (like a bpa-free nalgene plastic container), and put THAT inside a zip-top plastic bag (at the LEAST) but perhaps wrap a towel around it first (in case it does pop open, so the liquid doesn't saturate your suitcase, etc.) and maybe even put it inside another container with a good seal. THEN I'd make sure to label all the containers and outside containers, etc. WELL with exactly what you have going there. Hey, maybe even carry a copy of your order info from when you bought them (and is Nourishing Traditions too heavy to carry on? Ha Ha) or something so if they arouse suspicion, you'll have some back-up documentation.
FWIW, kefir grains do NOT appear on the list of 'prohibited items' by TSA:http://www.tsa.gov/travelers/airtrav...d-items.shtm#9