[Bookmark] Sweet n' bloody tea

See if any office supply stores near you offer laminating services. If you use a service, you'll be able to laminate your bookmarks and see if they sell well before committing to buying your own laminator. In the long run, having your own is cheaper, but it could also be a waste of money if the bookmarks don't sell well. Even if you decide to do custom bookmarks for people, you can still use the service between con days, or have someone run and do it for you same-day.

Also, when laminating, you'll likely have some space left over on the sheet where no bookmarks will fit. Make some 2D keychains or charms and put them there. Make that empty space into something sellable ;D

Great idea with the glitter on this one! You'll probably want to do more stuff like that for non-custom bookmarks. It's awesome to get an original drawing as a bookmark, but a lot of people don't really appreciate the value of that. If you want to be able to charge more for the bookmarks than printed ones*, you'll need to add things to them that can't be reproduced in prints, like glitter, foil bits, relief work, etc.

* I hope you'd be charging way more for these than printed ones! Don't sell yourself short. Charge for the time you put into these and your skill level, not just the materials.