You are probably not using enough glue or not letting it dry long enough or both.

I use a bottle of Elmer's rubber cement at home. It's cheap and it lasts a long time. I've been told that it can't work since it's chemically different, but I haven't noticed that it doesn't work. I try to avoid opening a tube of glue because it does dry out at the worst time. I try to keep a careful watch on my tubes of glue, because I don't want to make a discovery on the road.

I normally carry one spare tube and a patch kit so that I'm ready for more than one flat.