We got the two foot plastic folding step stool for bunks which sticks away under table, etc when not in use. My wife uses Command Hooks like a boss for most of the adds below.
I'll try to remember the biggest adds, mods:
Gas shocks to raise bed platform
Shelf which raises, lowers on end of cabinet for more counter space
Canvas shoe bag on end of bed
Another hanging shoe bag on bathroom wall behind toilet for toiletries, meds, first aid
All sorts of over door hooks for potholders, hand towels
Large towel rack over bathroom door for bath towels
Collapsible canvas totes for kids clothes to keep in bunk areas
Canvas baskets for overhead storage in bedroom
Small baskets on bunk walls for kids phones, ear buds, etc
A metal shower organizer which we put on wall by vanity for toothbrushes, etc to use as medicine cabinet
We used various wire shelving units inside cabinets to maximize storage of food, plates, etc
All the little stuff underneath the trailer is in plastic totes with lids
(Did I mention my wife has a certificate as a professional organizer? )
We also got a drying mat and small dish drainer, set of runner and rugs for floor, and drying bath mat.
I'm sure I'll think of more later!