- Carry a small umbrella and light raincoat in your bag. You don't have a cart to take cover under, and these add very little weight compared to the benefit in a storm
- Get a comfortable bag that is lightweight and easy to pick up. Something similar to the Sun Mountain Three 5 bag, which is light with a good strap, is ideal.
- Make sure your bag has a pocket for a water bottle, preferably insulated, so that you can easily store it and carry it with you on the course.
- Make sure your golf shoes do not rub your feet weird when you walk, or you'll have an adjustment period before you create calluses.
- Set the bag down whenever you can. If someone else is starting their routine, set it down quietly. If you will stand in a spot for more than 15 seconds, just go ahead and set it down.
- Walk straight to your ball (even slightly past others') and set your bag down to wait for your turn whenever possible. In high-school tournaments the general rule is stay out of a 30* cone in front of people when doing so, but do so at your own risk and stay aware.
- Set the bag down between the flag and the next teebox when you are putting, it saves a lot of time.
- Carry too much weight. Old yardage book? Toss it! The same goes for extra balls (you shouldn't need a full dozen) and various widgets that invariably make their way into a pocket somewhere.
- Carry with only one strap. Unless you're moving it a short distance (think 20' or less) you should put both shoulder straps on. It's more comfortable and it saves your back.
- Look for golf balls while carrying a bag. If you need to look for a ball (yours or another player's), set the bag down first. Why walk extra with the bag when you don't need to?
Basically just keep the weight of the bag down and minimize the time that it's on your back to the time you spend walking between shots and you'll be fine. That said, a pushcart is an excellent option if you can fit it within your budget. I would absolutely use one if I was able to in tournaments, it provides the benefit of a caddy carrying for you without the extra cost per round.