My general approach with glue is to try to buy really small tubes (Home Bargains occasionally do a good value kit with a couple of tubes, a selection of patches and some crap tools for a couple of quid), and carry a new unopened one on the bike. They're not immune to manufacturing defects that cause them to dry out, but they tend to last much longer than opened ones.
Once used, the open tube goes on the shelf for use on any subsequent puncture repairs done at home, and a fresh one in the kit.
In the spirit of this thread, I gave my Road Morph a workout earlier.