A no brainer idea for most affiliate owners is to give away a shirt for new members. Seems simple and harmless. “Here is your goodie bag and welcome to the family!”. Unfortunately, it’s not as simple as giving away a free shirt.
It trains new clients that apparel and the items in the goodie bag have no value. Simply: if it had any value, you would not give it away for free.
You will need to carry inventory. You’re not going to find any vendor who is going to print 1 small tank top or one 2XL tee every time you need it.
If you carry inventory, it will be nearly impossible to forecast and project sizing. So you may order 150 shirts, sell out in a particular size, and still have 80 shirts left. You’ll need to reorder in smaller amounts to ensure you have something for everyone.
A better strategy is to give new members a gift card. They can use it on whatever they feel is best- supplements, apparel, personal training.