Best time to get a spare alternator belt is next time you have the prop off. Put an extra belt behind the flywheel and secure it with tie wraps so when you need a spare you do not have to remove the prop on a trip.
Other people might say to take a replacement drain...
If you are worried about an alternator belt failure........ this https://www.google.com/search?q=Power+twist+link+belt&ie=utf-8&oe=utf-8 will work to get you home.
It is not a replacement, just a crutch that can be installed with no tools if you had to.
Many bearing shops sell this by the inch.
Flat tyre - in long grass on an RV8. Try and get a efficient system to jack the aeroplane...not easy.
Flat battery..we now have an Anderson connector in the luggage bay to jump start, otherwise in the -10 you have to take the rear panel out to get at the battery..a real pita
Also we now have a "below 12 volts" flashing light which is on if the bms is on and the engine is not running and charging, a good visual reminder.
You will never have tools for everything, preventative maintenance is your friend
....Most places at least have a store that has tools, if not someone on the field....