What do you mean you've never used an old drawer as a shelf? Well, if you're an avid thrifter, you might've drifted into the field of garage and estate sales as well. Any thrifter looking for another hobby to add to their repertoire with a group has considered "fixing up _____" before. Now if you're like every other human on earth, stuff probably happened and you never got to start your illustrious career fixing up furniture. But if you follow this nifty upcycle, that side table you already bought won't go to waste.
Get some vinegar and water and wipe down the drawer. This will get rid of the excess dust and dirt. Depending on the look you want, you can remove the bottom of the drawer to expose the wall. Or you can get some acrylic paper and paste it to the bottom of the drawer, giving it a cool contrast with the rest of the wall.
When it comes to filling drawer shelves, you can add another shelf in them so they can be used as a tiny bookshelf. Or you can add the extra plank across the opening so it functions like a cubby. This idea is great if you want to store things that tend to tip over like books.
Drawers shelves are best when they're used to display things though. Drawers as shelves are great as an aesthetic, So things looks extra cool when you put things in them. If you want things to stay cohesive, pick three keywords to create a them around, and shop for trinkets that fit those keywords. You'll end up with an awesome display piece.