[QuercusMax]

I always just used a pencil.

[TeMPOraL]

I usually had neither on me when needed, so I just used my pinkie.

[Anarch157a]

That's good for small rewinds, but with a Bic pen, you can rewind the whole tape as fast (maybe even faster than some) ad a tape deck. Just slide the pen in the spool and start spinning the cassete.

Like this: https://m.youtube.com/watch?v=yk8v9Ijp1So

[QuercusMax]

That worked too, was just a bit more uncomfortable.