I'm taking a
loungefly this year. In the past, I've done no bag (dad had the money and carried what I needed his cargo shorts pockets), a purse, and a full backpack. The full backpack is just too much on some rides. The purse is often not big enough for things like rain ponchos, body glide, food powder, sunscreen, etc. It also can leave your posture unbalanced, which can cause pain later in the trip. The loungefly size bag is a good compromise for me because I can fit what I normally need the most, but you can wear it as a backpack for even distribution of weight. You can get cheaper but similarly sized bags.