Your local music shop, or even a large supermarket in my area, has a little stick-on that's sort of "pick shaped" and about 3/8 inch thick, with a spring loaded "button" so that you can slide about 5 picks or so into it, on top of the button, and the spring keeps them where you can just strip one off the top. (sort of like those cheap plastic "coin dispensers" you may have seen before the cash register delivered the change automatically?) They mount with a "foam strip" pressure sensitive adhesive. Might be about $3 (US) or so.

Can't recall who made them, but they're not hard to find in my area.

They're a little large for a mando, and although I did stick one on one of my old ones, I don't think I'd recommend them for that. They're just large enough to hang a little over the edge on a mando. They should work okay for a guitar, if you don't mind sticking something to yours.

Some guitar players in my area stick them on the body near the base of the neck; but at the end, between the gears, is the more usual place. Of course, everybody has a "favorite," and it usually just tucks between the strings, so this jobbie is just for spares for most users. (but only holds about 5 or 6 med/heavy picks)

John