I’ll call these table-top extenders with an outlet strip because I don’t know if they have a name. Whatever you call them, they are useful. They provide a place for all the little things that accumulate on top of the table, and having the outlets available is very handy.
The back is ¾” pine. It’s inexpensive and can be shimmed to fit securely between the wall and table. After the back was cut to size (leave it a little longer than you first figure – it will be easier to work with and you can cut it again later), I put the pieces that form the groove for the table top in place and drew pencil lines so I would know where to glue them. If you do the top one first and secure it, the bottom piece will be easier and you'll probably get a better fit. (You probably want to have someone help you hold the back against the wall while you do this.)
It started out as one long piece, but there was not enough room on the ends to slide it into place. That’s what they make saws for. It actually works better being in two pieces. We leave the halves separated by a couple of inches and drop the electrical cords over the end of the table so they are out of the way. If you put the outlet strip in the middle you will have room for those odd shaped plugs.
They are secure when in place. It’s a tight fit with no binding. I don’t leave them in place when we are moving because they might chafe the wall.
That little box below the table is a shoe-shelf.