Lawn chairs are the most common way of solving this. Do not sit on the benches or chairs around the arena. These are reserved for the dancers only. Do not touch or move articles or regalia that may be left on chairs. Ask permission before taking pictures of dancers.
Many people are sensitive about pictures, so it is always good to ask.
Some articles are sacred, especially the eagle feather. Never touch an eagle feather. If you see a feather upon the ground then bring it to the attention of the arena director. Do not pick it up. Donate money to the Drum.