Ironing isn't the only way to get rid of wrinkles. If you're traveling without your iron or are just too lazy to drag out the ironing board, your clothes don't have to look like you've slept in them. Some people are sensitive to the perfumes and dyes in fabric-softener sheets, and others are concerned about the potential environmental impact of the sheets, so try out these low-impact (and free) steps first.
If you haven't yet taken a shower, give your clothes a good shake and hang them in the bathroom near the shower. The steam from the shower will relax the wrinkles.
If this doesn't solve the problem, dampen your hands slightly and run them over the surface of the garment, smoothing out the wrinkles as you go. Wait a few minutes, allowing the garment to dry. Alternatively, use a spray bottle filled with water to mist the garment lightly instead of wetting your hands.
If these steps still haven't fixed the problem, dampen the garment slightly and place it in the dryer with a fabric-softener sheet (check the garment's label first to see if it's safe to put in the dryer). Tumble dry for a few minutes until the wrinkles fall out.
To avoid wrinkles in the first place, don't overload the dryer, and remove the clothes from the machine when they are just barely dry.