making a box and putting stuff in it?

When you buy an item in a store, it is usually in a box you have to open (which confused me no end, the first time). But it's useful since a small item like jewelry, or an invisible item like a script, can easily get lost or be invisible if it doesn't have a pick-uppable container...

So how do vendors make a box, and put their goods in the box? I don't see "box" in the create dialog...can any solid be a box?

Yep. Any prim you create can hold things, but yeah, cubes are the most common. Why? Because people expect to see a box.

Although in RL some clothing is sold in cylindrical containers. That might be interesting to see in SL.

Maybe SL vendors should try selling stuff in sculpted objects. Nowadays design is being used in all sorts of RL packaging.

I've seen cylindrical and pyramidal packages in SL as well. Single prims have the advantage of conserving resources (hey, SL eco-friendly packaging), though of course vendors are even better, depending on the number of items and vendor design.