We have an odd-number group trekking together, what sort of accommodations can we expect?

Inca Trail Campsite
Inca Trail Campsite

As an odd-numbered group, you will have an extra passenger who will have to abide by the single passenger policy for accommodations:

You can request private accommodations and you will have to pay a single supplement fee. This applies whether you are camping or using lodges/hotels along the way. Tents and hotel rooms are typically designed for two passenger use.

However, most travel providers give single travelers the opportunity to share accommodations with another traveler. Travelers must indicate that they are willing to share accommodations well before their departure date. With many providers, if another traveler is not found for the shared accommodations, then the single traveler will have to pay the single supplement.

Hotels sometimes have triple rooms, which can be a good option for an odd- numbered group.