Old books can be tricky, and they get heavy…
Old carpets on the floor, or simple throws. The same over boxes of things: That big plastic box you brought your kit to camp in, inverted and with a blanket over it, instant table or seat.
Sheepskin rug? Or similar looking, over your bed or similar?
You can get collapsible multi-part candle-holders, or ones that hang from hooks or tent-poles: might want to use LED fake candles in them though (also good).
Pennants, tapestries, paintings, trophies… weapons/armour racks (collapsible for transport and indeed authenticity).
Some IC eating/drinking materials? Tankards, goblets, wooden (or plain ceramic) plates? A bowl or two of IC nibbles (fruit, nuts, bread rolls?)
And if you can store the OOC stuff out of the way (under a table behind the throw, concealed in a large canvas sack) you’ll have less to break up the immersion.
Police your IC tent for beer cans, plastic packaging, and people character packs… I find they tend to accumulate in the IC areas…