The most direct and easy way to encourage customers to order your accessory for your product along with your main item is to do a manual bundle (not a virtual bundle).

I agree. Virtual bundles are not useful.

You need to "make a new item" by combining your accessory and main item into one. You can do this multiple ways.

Lets pretend you are going the poly-bag route. You have to take your main item and your accessory and put it in the poly-bag together. Set it on a table or something and return to your computer. Once at your computer you now need to "make a new item". It should have a similar title to your main item but include that this offer includes a "Bonus accessory". Once you get to the part where you need an ASIN, you should request a GTIN exemption so it can be ASIN only. (no UPC needed).

Once your "new item" is created, you have to get the product ID labels (FNSKU). Once you get this barcode like paper, you should return back to the table where you set down your new item and tape this barcode onto the polybag to identify your new item. Do this for a couple of units so you can have a box with like 10-15 units to send to Amazon FBA (if you send it through FBM you do not need to do this process...you can just put both items in the same shipping container and send it off its way).

In most cases, you can merge this new item (new detail page) to your main detail page and have it be a variation. So your customers can pick from your main item or a featured bundle. Its a great way to boost sales and to get people to buy your accessory.

I admit, its easier said than done as I have been doing this for years and its second nature. Maybe a mod can provide more literature?