I often find the best use of my miles is for very short, otherwise very expensive trips. This may be more of an issue in Canada than the USA, but I'm not sure.

For example, a flight from YOW to YTS is only a distance of about 420 miles, but flights up there regularly range around 1000 CAD (with advance planning). Because of the short distance, it's only 15k to pay in miles.

Second choice would be as Ericka said- F and J tickets that we wouldn't be able to afford otherwise.