Plywood
Everything is built using 1/4" and 1/2" plywood.
The floor is 1/4" marine plywood, see the flooring section for more details.
The cabinets / countertop / table / seats are built using Ultralight Plywood, which is quite a bit lighter than Baltic Birch. Their 1/2" plywood is significantly lighter, which was nice since I could stress less about the weight and use 1/2" for most of it.
The seats are exclusively built with 1/2".
The table and counter are 1/2" plywood, then stained and sealed.
The cabinets are primarily all 1/2" plywood except the one front side piece at the entrance of the vehicle.
The drawers are 1/2" plywood bases with 1/4" plywood sides and faces.