Hmm,in my opinion that should be electronics and gadgets because we can often see some deals online and also clothes I think is a big one.That should be the top selling products as far as I'm concerned.
But to my preferences, the best thing to offer for bitcoin should be digital goods or services because you can be able to sell and deliver to anyone in the world but when you go for other goods there are chances that you cannot be able to ship to all parts of this world due to certain security reasons.
Digital goods were the most selling things for bitcoin in online stores as well openbazars. Recent days more online stores were improving the shipping processes in collaboration with several other partnership's. This might help users to buy their desired products soon.