Here's a short list of organization products I've found useful in my minivan camper. I'll add Amazon links to illustrate, but try and buy local and/or used if you can.

Folding Storage Footstools (https://www.amazon.com/gp/product/B07XHX9M26/)
These are the same size as cheap folding cube organizers, but are sturdy enough to store heavier objects (such as books) or to use as extra seating. I also flip the top over and use it as a tray.

Clothes Storage Bins (https://www.amazon.com/gp/product/B09YXXS3LW/)
These are excellent for storing clothing and are available in many different styles and sizes. I have four stacked in a 2x2 block and secured to my shelving with 2" velcro straps.

Small Hanging Drawers (https://www.amazon.com/gp/product/B077SPWG29/)
I have two of these hanging under my bed to fill out a small unused space.

Hanging Shoe Organizer (https://www.amazon.com/gp/product/B08D983YS9/)