I use standard storeage crates, each 600mm X 400mm as the base for a bed.
Theses crates are available in various depths and can be stacked if required, 8 are suited for a standard double bed, cover the crates with piece of plywood of the correct size for a standard spring or foam mattress.
If desired the crates may be concealed by a curtain or valance attached to the plywood, though I did not bother.

One could store tinned food and bottled water thus, though I stored blankets and clothing, thereby freeing space elswhere for food.

These crates are available with ventilated sides, best for avoiding damp or mould attacking clothes and linens, or with solid sides that would resist vermin.