This is a little trick I learned from my mom.
It worked so well, especially for "cranky" fingers, that I invested in a new basket of them.
I've found that clothes pins are often much easier to pinch open than the official bag sealers, at least the newer (more cheaply made?) ones. Plus, they're more economical than some of the fancier bag sealers.
If you try it, please let me know what you think.