The one-slice type with a gauze to spread the heat and glow red, and a few chrome bars for the bread to sit on. As sold in all good camping shops, and most crap ones, even Wilko. Pay no more than £2, because they burn through eventually.
These actually work, provided your stove has a large diameter burner - some small folding gas stoves just create a small hotspot. Toast takes about 10 seconds per side, so you get it crunchy on the outside and soft on the inside. They are so rapid that you can cook 8 slices of toast for a family as fast as they can be eaten. They also work on the gas hob at home if you want to practise.
Not to be confused with the "pyramid" toasters for four slices at a time. These don't work.
