So when I go to the beach, I lock the actual key in the glove box and take the valet key with me, locking the driver's side door.

But now there is something that is preventing the key from going into the lock more than half way. I don't know if this is salt or debris (the car is in Florida and this is the first time I've tried this in a while). It is possible there is a piece of sand in there. I was able to jiggle it enough to eventually insert it fully, but it was a pretty dodgy situation for a few minutes.

Any advice on what to do here? Would it be a bad idea to either oil the key or spray some WD 40 on it? Or perhaps spray some type of lubricant into the lock if I could manage to do so?

 

The best lock lubricant is powdered graphite. It comes in small tubes and is available at any hardware store / Lowe's / Home Depot etc. Place a dab on the tip of your key, insert it, and work the lock back and forth. Pull the key out and repeat the process. Be sure to wipe your key clean before you put it back in your pocket.