I'm something of a cyclist and I drive on a lot of roads where there are cyclists all the time. I keep meaning to make sure my car is stocked with some helpful bike tools or a spare tube or something. I need to get on that.
You might want to have tubes with both Presta and Schrader valves (to match the existing tube on the other tire). Theoretically you could use either, but some rims might have a hole that's only small enough for a Presta valve (so I guess that makes Presta slightly more compatible in an emergency!).
I agree that there's flexibility in the sizes. When I wanted to stock up my work's garage with spare bike tires, I got four kinds in total (basically a small Presta, a small Schrader, a large Presta, and a large Schrader). This officially covered pretty much every common road and hybrid or mountain bike with something that was officially rated or matched to it. But yes, as far as I know, one could probably get by in practice with fewer than that and use things that are officially slightly mismatched.
Specifically, I got the Specialized "Standard Schrader" 700x20-28c and 700x28-38c, and "Standard Presta" 700x20-28c and 700x28-38c tubes (the smaller ones more likely for road bikes, the larger ones more likely for mountain bikes). These are about $8 each in the U.S., so a total of about $32 for the set of four. 700c is increasingly common, although there are several other diameters that have been or are being used.
Just having a bike pump can be pretty helpful in many circumstances!
Same. I'm tempted to throw in a couple of spare tubes in the little pocket things between the interior trim and tail lights, where just now I keep a spare fanbelt, too.
I usually have stick-on patches and a bike pump as well as the normal Landrover-fixing tools, because you can have a toolbox without having an old Landrover but you can't have an old Landrover without having a toolbox.
