When making a river crossing, trekking poles can come in handy in several different ways. Every crossing is slightly different. Some instances may be easier and allow a person to step comfortably from one rock to the next, but in most cases you will have to either hop from one rock to the next or take your boots off and cross in an area where the water is lowest. Trekking poles help to give you balance when stepping on slippery rocks or river bottoms. As the weight of your pack shifts and the water pulls, sometimes the only things keeping you up are sturdy pole plantings in the river bed. A trekking pole can also be used as an extension of your arm when reaching to give someone a hand, for instance if he were leaping from the last rock step to the river bank.
A tarp can be set up almost anywhere, thanks to trekking poles. If there are no proper trees to use in the construction of a tarp covering, then you can make a lean-to structure with your tarp and poles. Secure two corners of your tarp to the ground and prop up the other two with your trekking poles. If you have adjustable poles (these are the kind to have), you can decide how tall to make that side of your shelter.
Wilderness First Aid
Trekking poles can create a leg splint if need be. Anyone who has been through a Wilderness First Responder certification course knows that in emergencies, unlikely items may work in the backcountry. Jacket sleeves can be morphed into an arm sling, backpacks or crazy creek chairs can be used for leg splints and trekking poles can also help in this situation. A sleeping pad and a trekking pole are two things most backpackers have with them; when deflated, a pad can be wrapped around the injured leg and then tied tightly around the leg and trekking pole (with clothing or rope) to keep it stiff and straight.
As you are hiking along with your trekking poles, you can use to create noise in addition to balance, terrain navigation and joint support. If you are in bear country, rap your poles together here and there between steps. This signals to the wildlife around you that you are coming through the area. Most wildlife will hear the noise and move away from it. Walking silently can sometimes startle bears if they are near the trail, and if this happens they may become scared and angry.
There are of course other little uses for your trekking poles. Prop your trekking poles between two trees and use them to hang-dry your gear. Use them to test snowpack or the ice at the edge of a river in winter. It's probably not impossible to spear a fish with a trekking pole, either.