I'm a dedicated fountain pen user. I carry the pen nib up, tap the barrel a couple of times to make sure the air bubble is between the ink and the knib. When I remember, I put the pen in a cigar tube. Sometimes, it goes in a freezer bag with all the other "unexpected behaviour" bits. I've frequently omitted steps 2 and 3, but never step 1 and haven't had a leaky pen. I have had a biro go all unnecessary on me, though.