Tabitha....Chalk paint would be to clean and paint which is probably the easiest..otherwise, you can clean sand and use most any paint.
You might find some inspiration in the way this wood letter was painted https://familyfocusblog.com/diy-letter-decor/
Tabiltha: I agree... chalk paint is the easiest paint to work with... and requires no special priming or preparation.
I have some of those boxes too, I have painted them with Folk Art or Apple Barrel paint. I have also used Folk Art Ultra Dye and Folk Art Wood Tint and those soak more into your wood and are quite beautiful. All you need to do is paint those - they're ready to go. No prep work needed.
I would try some chalk paint