I don't travel with Loaded magazines...test case for the Anti's just waiting to happen if you do.
For how many.....
There's a couple of 'Formulas' I use.
5 Mags: 1 in gun, 4 in magpouches
6 Mags: 1 in Gun, 2 in Magpouches, 3 for a spare set
These two formulas I use for my 9mm 1911's.
For my HK P7M8's I kindof went a bit far...
3 guns with 2 mags each...I keep the mags in the box. I bought 3 used P7M8 magazines with a 10 pk of Wolff Magazine springs (range use mags). Then over a few months I bought 6 more NIB magazines. P7M8 magazines are so robust, unless you abuse them you just have to replace springs.
Other guns in my collection have between 2-4 mags each.
Of course I'm always of the mentality that if the Gov't ever shuts down import of guns/and parts, I'll have enough to keep going....'
P.S. You should see my spare parts box for my P7M8's...spent a fortune on those!