| One of the most valuable emergency kits is a puncture repair kit - especially when you plan on leaving pavement. The kit (available in most auto parts stores for about $8) consists of extremely sticky self sealing strips (X), vulcanizer (no picture) one tool (1) to enlarge very small holes (cactus punctures) and a second tool (2) that is used to stuff the plugging strip into the hole.
A pressure gauge is helpful but not essential - guesstimating works quite well. If you plan on buying a gauge, get one that measures from 0 to about 50 psi. It will be more accurate in the area we need (15 to 35 psi) than units that measure from 0 to 100 psi.
I personally do not like "spare tires in a can". They will only seal punctures in the tread area and leave sidewalls untreated. Unlike the self sealing strips (which create a semi permanent fix) the stuff in the can needs to be removed as soon as possible. By the way, tire shops hate that gunk in the tire.
Since the self sealing strips plug sidewall punctures perfectly and permanently you can keep your tire instead of throwing it away (sidewall punctures cannot be fixed with inside patches by your tire shop).
Another plus: Even very large holes can be fixed (I have fixed 2 inch long gashes in the sidewall successfully) by adding more and more strips until air stops escaping.
Here is my only negative experience: Goodyear tires love to develop punctures in off-road environments but hate to be plugged - they "spit" those plugs out within a few minutes.
A regular bicycle pump (about $10) will do a beautiful job. It's fast and gets you valuable exercise. Plug in compressors have a tendency of failing.