Any decent 2-part paint
such as the polyurethane
paints. Awlgrip is good. So is Dupont. Also 2-part epifanes which is a little cheaper (but still expensive.....). I've just put some of that on my topsides but it hasn't been on for long enough for me to be able to give feedback on how it lasts. You can buy 'anti-skid additives' or just sprinkle on some sand. Do the first coat, cover with sand. Once it's set brush off the surplus sand and cover with another coat or two. I used sand-blasting sand like this on one of my boats. Very good non-skid but i wouldn't want to fall over on it!
There are also other options. A friend of mine has something called 'tread master'. Very good product - comes in sheets
and you just cut them to size and then stick them down with an epoxy-based adhesive
(you could probably also just use epoxy
resin with a tiny bit of filler added to bulk it up a bit but i haven't tried it...... It's not hard on your skin if you fall on it and it's very good anti-skid even when soaking wet. Planning on getting some next year.