The simple inner tube - a vital piece of kit, and every person should have a spare one in their tool box.
Tip: When you get a puncture, swap out your old tube for a new one, but patch your old tube (if possible) and this will become your new tube for the next puncture. Saves you money, and prevents waste.
You will need to know your tyre size - check the sidewall of your tyre. It will have a few different numbers saying something like 700 x 28, or 26 x 1 3/8", or 26" x 1.5, or 27.5 x 2. Another helpful number that denotes tyre size is the ETRTO number, written in a format of XX-XXX, like 28-622, or 37-590, or 40-559, or 50-584. Believe it or not, those numbers I just listed actually correlate with the previous list of numbers. The first number is the width of the tyre, the second number is the diameter. Good ol ETRTO to the rescue!
You will also need to know what kind of valve you have - Presta or Schrader.
Any questions - need help finding your tyre size, or don't see your size here? Just email us: firstname.lastname@example.org