A cleaning set. For a handgun, some handgun sized disposable barrel swabs, some oil (I prefer Hoppes 9 for general purpose), rags, and some q-tips are usually enough. For some guns like Glocks, a little bit of metal polish applied to the trigger mechanism can make them a bit smoother overall for not much investment.
A roll of painter's tape is good to have for a range bag to help plug up targets while you're shooting to make the targets usable a bit longer. Sharpies also work, I just prefer tape. It also works to put up targets if the range's staple gun or target clips aren;t working.
Targets. You can go from buying a fancy set of splatter targets to just printing off some on normal paper.
For handguns I have not really ever used speed loaders for the magazines. I just haven't felt hindered by putting rounds in manually, but if you want a little help it's out there.
You may want some way to adjust the sights. This can be a set of small precision screwdrivers, or for factory Glock sights- a tap and mallet. Eventually with the optics you'll probably want allen keys or star keys to make adjustments.
The investment that is you should learn both good shooting and responsible habits. Ranges tend to have introduction to shooting either as group classes or one on one, and getting those basics down may seem boring but fundamentals are important for everything else. I'd even soft suggest looking at a CCW course, even though you don't intend to carry, since the CCW courses do focus more on crash courses of legal and storage responsibilities. It can't be bad to have those things in your head.
After that point, regular practice is just something to keep the rust off your abilities and familiarity with handling. I have a habit of sharpie marking targets with dates/distances/drills/gun used and taking photos so that I can record long term. It helps identify certain trends where I need to work on them.