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.
That is certainly true, but not everyone also requires all digital items. Because the bitcoin can be used for those who want the real stuff, as with many I meet very expect there are online stores that want to accept bitcoin so they could search for items needed for real world use. And instead of becoming a benchmark for sure if we use the bitcoin to receive payment of digital goods will be successful