Most OSR games come with decent guidelines for determining treasure, valuables and magical items, but what about "other" things?
Here's a quick table with random things that could show up in a monster lair. I've leaned towards things that might be interesting, in a campaign and plot sense, rather than "2D6 bones and a painting of a dog".
Some of these results may seem odd for certain monsters. Give it some thought before rejecting an option. Maybe a really unexpected and clever explanation might reveal itself. If not, toss it out and go with something else.
How many rolls you make are up to you. A "normal" monster encounter might have 1 item, while a tribe of humanoids might warrant 2-4.
Likewise the exact amount of a given result is up to the DM. 1D3 might be suitable for a smaller encounter, and 1D6 or 2D4 for larger situations. Use your best judgement.
1: Captives, may have information
2: Captives, suitable henchmen or player character replacements
3: Finely crafted weapons (double value or roll here )
4: Finely crafted armour (double value or roll here )
5: Maps of local area
6: World map with unknown location indicated
7: Collection of keys (20% chance of fitting any given door)
8: Letters indicating connection to random faction in the campaign world
9: Holy icon of ancient religion
10: Strange fungus (effects like random magical potion when digested)
11: Letters from previous victims (may indicate sub plot generated here )
12: Stash of adventuring equipment
13: Large stash of ordinary weapons and armour
14: Edible food supplies
15: Captives, useless but may give reward
16: Unusually large amount of treasure (roll twice for all categories)
17: Letters indicating bigger plot (invasion, infiltration etc)
18: Healing herbs and plants (examples here )
19: Entrance to secret room or cave
20: Entrance to secret dungeon complex