Dear Dungeonmasters,

This could really also count for creatures like giant vultures/eagles/owls, ect. My party may choose to venture up onto a mountain soon where they have the chance to encounter an temporarily abandoned Roc nest. That nest will remain abandoned until later in the day. Depending on when the party finds it they may be able to snoop around in it for a while.

Aside from a Roc Egg /  Hatchling, which is of course the purpose of a nest, what could my party encounter inside the nest?

Specifically, this creature lives far out into the wild with very little to no civilization around it aside from some tribes of goblins and orcs and alike. 

Id love to hear any and all suggestions!

Bones from the creatures rocs eat. Traditionally, this includes elephants, so, if the area's right, there could be a lot of ivory in and around the nest, though looting it would take a fair amount of time.

Birds often have mites that live in their feathers. Imagine how big the ones that live on a roc are. Now re-chrome a giant spider and set up the fight. :)

What did the roc use to build its nest? Anything interesting in there?

Is there any creature that tries to steal roc eggs?

You can always hide a magic item or trinket that could come up later in the game as something that an NPC lost on a journey or pilgrimage. Any clothing with a recognizable insignia will make your party go crazy as they ask, "What was [INSERT GOVERNMENT/CORPORATION/ENTITY NAME HERE] doing all the way up here?"

The general likely story for 'how did weird stuff get up here' is that a Roc picked up some prey and carried it to its nest (probably to feed hatchlings, otherwise it likely just eats it where it caught it, but some birds reuse nests from year to year).

I’m a big fan of including the stuff normal folks and adventurers would have on them in these sorts of situations. So definitely a trinket or two, and then some handful of the following:

alms box, amulet, arrows, bell, bit and bridle, block of incense, blowgun, blowgun needles, boots, candle, case, map or scroll, censer, chalk, crystal, dagger, dart, dice set, flask or tankard, flute, helm, ink (1 ounce bottle), ink pen, mess kit, mirror, steel, oil (flask), parchment, perfume (vial), piton, playing card set, pouch, sack, sealing wax, shawm, signal whistle, signet ring, sling, small knife, soap, songhorn, string, tinderbox, torch, totem, vial, wand, whetstone, yew wand, any variety of tools, or gems valued at 10 gp or less.

If a nest with hatchlings or eggs about to hatch, you could have a creature or two still alive there, brought by the parent for the hatchlings to practice hunting/killing. Maybe the hatchlings aren't hungry at the moment or it managed to wedge itself somewhere they can't reach.