Yes, paperclips are wonderful for this purpose, especially so when used on one's fly zipper as they've a low profile and can't be seen.

The best paperclips for this purpose are the V-shaped type that are narrower at the top. They've saved me from having to replace a zipper on a number of occasions.

If you read my comment about washing powders attacking the crappy alloy material that's so often used in those pull tabs and causing them to fail then a paperclip is the ideal solution.

Split rings (key rings) work well in my experience.

Yes, I've usually just used a short piece of string. But I'd still like to be able to replace them with a proper puller.