A couple of very cheap sectioned trays. Shallow enough to make grabbing tokens easy and enough sections to organize them. We use these for pretty much every game with tokens.
A side-table to help deal with table hogs.
A couple of those foldable dice trays. I don't actually use them for dice but as a flexible funnel when bagging things.
Notepad, pencils, eraser
An empty tea tin. I use this for some games where you frequently draw items from a bag because it's a lot faster.
We usually sleeve games once its obvious we are going to play it a lot. Terraforming Mars, Clank, Dominion, Ark Nova all come to mind. But sometimes the sleeves are rather sticky. It feels like good sleeves are super expensive.
Dragon Shield Matte are amazing! IMO I haven't felt an experience of holding cards like Dragon Shield (and I've used a lot of other sleeves for games that don't fit the standard card size). Just my two cents.
My favourite cheap accessory is silicone muffin cups. Available in multiple colours. Fits all your different resources. I think nearly every second person in our club has some. Extra nice: cups with a fold halfway up. Perfect to make half cups for fewer recourses. When not in use, make cupcakes.
We do have a 3D printer and I love improving my games with all sorts of little things. I did also print some 1-part, 2-part, 3-part and 4-part stackable, multicolored trays which I love and use for many game.
And I have also folded some origami for Everdell which is a great addition and still all fits into the box:
But my favorite is our Burgundy Hexagon - it holds all the components of the game and includes also two dice trays. I would not want to play it without it, it makes playing much more fluid. The downtime inbetween phases is super short.
X-trays to store game pieces is life-changing. The lids hold on well and they are stackable. They come with me for any game. And they are like $1.50 each