Tote bags are an easy to make one size fits all merchandising option. It is overwhelmingly the item that my fans want to see available on Amazon and in other storefronts. I have picked Amazon Merch as my POD shirt service for a variety of reasons, but limited number of sizes and products were on the "cons" list.
Most of my fans want to be able to buy tote bags because they already have a lot of shirts, because they don't like printed shirts, because the Amazon Merch sizes are too small for them, and/or because they KNOW that, when they buy a tote bag, that tote bag will fit them. There is basically no chance of a tote bag NOT fitting a user, making it a purchase that users are likely to buy online because it does not require consulting a size chart. Because tote bags do not require a size selection, there are fewer clicks between a user reaching a product page and buying the item, and less time spent looking at the item. Tote bags are even more of an impulse buy than novelty shirts. Given that tote bags are not as easy to find online as shirts, this leads to loads more sales for both Amazon and Amazon Merch members.
Tote bags have the added benefit of not needing to be able to be washed as often as shirts, so the designs last longer and look better longer. Tote bags are always visible, whereas a shirt might be hidden by a jacket or other outerwear.
The overwhelming majority of my fans have voted for dark black totes, because the designs really "pop", and white tote bags are already common. Most POD places only print onto white or "canvas" off-white bags, so providing a black tote option would draw in more users AND more artists! Currently, the maximum sizes allowed are 3XL for men and XL for women. Many of my customers have specifically requested larger sizes (up to 7XL in women's), and due to the nature of my user demographic (plus size art), the overwhelming majority want a plus size option, and are not satisfied with a men's 3XL (the size is either too small or the cut is not flattering). The average American woman is now a size 14, which is already on the upper end of XL, and other shirt sites and print on demand sites offer larger options, up to 4XL for women usually. For these women, their current merchandise option is to either have me manually print and send them larger merchandise (not optimal), buying items that are too small and sewing them into other items, or just not buying merchandise. If plus size merchandise is unable to be provided for some reason (plus size being anything above an XL for the context of this post), a tote bag option would allow these women to buy an item that would "fit" them, as tote bags are unsized.
Ideally, of course, both plus size merch and tote bags would be available via Merch.