I generally don't bother with an Unusual Background requirement. Rather, I assume that most of what the reenactors do can be summed up under the skill Hobby (Chosen Period Verisimilitude) and justified through an appropriately crafted character background. I also tend to suggest that at least a few other points be expended to reflect other period skills that the character may have picked up.
For example, many of my own modern-day characters are SCA members (an easy way to get a
VERY basic grounding in medieval combat) and will generally have a point or more each in:
- Broadsword Sport
- Shield Sport
- Games (SCA Heavy Combat)
- Hobby (Chosen Period Verisimilitude)
- Savoir-Faire (SCA)
For a more in-depth character, particularly if he might actually have to use those combat skills effectively, I may raise the Broadsword and Shield skills from their respective defaults (and place a note in the character background that he is an ARMA member), add History (Chosen Period) and a couple of craft skills -- usually Armoury (Body Armor) and Hobby (Homebrewing) -- and maybe even invest in the Anachronistic Training perk.