Waxed cotton is beautiful and functional, but you've got to maintain it. Otter Wax is the brand I've relied on to keep my jacket happy.
Waxed cotton is cotton fabric impregnated with wax,making it water and windproof. One of my favorite jackets, a Belstaff Trialmaster, is made of it. This relic, from a time when motorcycling gear was little more than thick cloth and a prayer, is beautiful, but once every year or so I have to re-proof it. Finding a wax that goes on easily, looks good and lasts a while took some doing. I've settled on Otter Wax.
Otter Wax's heat activated formula goes on like a cream. You use a hair dryer to heat it, once spread on the fabric, to help ease working it in as you rub in soft, circular motions. I just use an old rag, but perhaps you know of some special tool. Otter Wax goes on evenly, and cures over night. You can then touch it up and try to perfect it for a factory looking job, I simply leave it be. The jacket looks better and better, the more I wear it.
I also keep a bar of Otter Wax in the cars (I split one bar between two.) It is handy for touching up spots that get rubbed a bit clean by a camera strap, or etc. I find the character created on the jackets surface, by these activities, makes me love the jacket more.
If you have waxed cotton bags or jackets, I suggest Otter Wax to re-proof.