Recs.
Updated
The Park Tool VP - 1 is a vulcanizing patch kit, that incudes six patches, some sandpaper and a tube of vulcanizing liquid. This is a standard patch kit that won't take up much space, and will save you a long walk in case you don't have a spare tube.
Specs
Pros
Pro A good basic patch kit
The VP-1 patch kit is very similar to the vast majority of patch kits. If you apply it correctly, and do a few extra steps (e.g., cleaning the area with alcohol after sanding, and clamping the patched tire tightly overnight), it will patch your tube well. It's reliable enough, very compact, and the vulcanizing liquid is good quality.
Cons
Con Requires extra steps not mentioned in the instructions to get the best results
The instructions in this patch kit mention the most basic, major steps you need to take in order to patch up a tube, but it doesn't mention the fact that you need to sand down the molding line of the tube.
As with most patch kits, the results you get really depend on how you apply the patch. For example, if you're stuck somewhere outdoors in the rain, it'll be much more difficult to get the sanded area clean and completely dry before applying the patch.
You really need to educate yourself on patching tubes, and then almost any patch kit would do in an emergency.