I've brought a small kit with me for a couple immersion events when asked to. Generally speaking, if immediate first-aid was not available. Granted, scope of practice will prevent you from doing anything except the most fundamental and very, very basic things -even if it is the correct thing to do.
Depending on the event, size of your kit, and what you're trained it, will really be the deciding factors.
Prodigal Sons Mess of Co. B, 36th IL Inf. Vols.
Old Northwest Volunteers
Agents Campbell and Pelican's Military Goods