It’s the three Reveller’s on the bridge next to the Half-Moon Mill? I have noticed them every time I pass the mill and have finished most quests now without finding a reason for them being there. Sometime one will offer me a drink other times they don’t have much to say at all. Is there a reason for them being there have I missed something or are they just scenery?
The Wiki should clear your question
The Revelers are three happily-intoxicated Nord farmers you may meet at random locations while traveling the roads of Skyrim. All three wear random farm clothes, carry two bottles of Honningbrew Mead, and immediately invite you to join the party.
Seems that there is a mini-quest that rewards you with a Charmed Necklace (it's explained in the wiki, so I won't excerpt it).