It's a variety of things.
"The activity of promoting the sale of goods at retail. Merchandising activities may include display techniques, free samples, on-the-spot demonstration, pricing, shelf talkers, special offers, and other point-of-sale methods"
That being said though, a lot of shoppers go in and arrange displays, hang clip strings, organize merchandise, give out free samples, stand around handing out flyers, being a vendor who delivers a truck load of merchandise and stocks shelves and so forth. I've done a couple clip strip and oil stock ones myself, but that's about it for me. I'm sure plenty of shoppers will share experiences. Good luck and Godspeed.