Given that the cost of checking a bag is more than an entire day's typical travel budget, you might want to use a few tricks to make sure you can get your bag on the plane without having to spring the extra money to check it.
Not all airlines measure or weigh carry-on bags, and some of them don't do it all of the time. Some weigh them at the check-in counter and put a weight tag on your bag, and some airlines wait until you are entering the boarding area to surprise you with the weigh-in. So even though it may not happen very often, you should be prepared to shove your bag in that little metal rectangle of proper carry-on dimensions to receive the approval of the scrutinizing airline employee.
Wear your heaviest and bulkiest itemsLayers are good for flying anyway so wear your long pants, a top, and light jacket/over shirt. Definitely wear your bulkiest shoes! If you're traveling in a modest area, you'll want to cover up anyway. This will save a good bit of weight and space in your bag. You can always keep a quick-change outfit handy and change either on the plane or once you land if your bulky outfit is too warm or uncomfortable for where you're going. But at least get on the plane with the bulky stuff, then once you're in the clear, you can change.
In times of real desperation, wear tons of stuff! You hear stories and even see funny YouTube videos of people wearing pants, a skirt, a few tops, a jacket, scarf, etc. just to get their bag under-weight. LOL You might look ridiculous but it might worth it to save a $40 checked bag fee!