Article:
D&D 4th ed: Random Encounter Motivations.

So your group of player characters meet some random person or person-like thing on the way from one place to another,

but what exactly is that person or thing doing at the time?
Was that Troll you just ran into carrying some sort of special equipment?

Are the Elves likely to demand you show them your travel permits?

Here is a table you can roll on to answer just such a question!

Actually, with some tinkering, this list could be adapted to very nearly any location, for some reason, I always imagine these meetings happening on the slopes of Mount Doom... I'm not sure why.

So without further to-do, I present the...

THE RANDOM ENCOUNTER MOTIVATION TABLE!
Roll 1d100.
01 : On a raid
02 : Stripping a dead body of valuables
03 : Arguing with a magic item
04 : Resting & recuperating after a recent battle
05 : Sitting with maps spread out, studying them intently
06 : Burying their dead
07 : On patrol
08 : Searching for an escaped captive
09 : Running from a patrol
10 : On a quest
11 : Returning home from a quest
12 : On a slave raid
13 : Marauding & pillaging
14 : Setting up a digging operation, with charted map
15 : Wandering, dazed and confused with a head wound
16 : Fleeing another group/individual
17 : Travelling to a widely reported event
18 : Hunting another group/individual
19 : Repairing a vehicle loaded with goods
20 : At war