Hey NavySeal,
I have done the same thing. I am kind of a piece junkie so when new editions come out, I often buy several copies for all the pieces. Of course, then I end up with too many of certain things. Even with the unit sculpts. I will want a lot of infantry, tanks, artillery, planes, etc. but not so much with capital ships, even for US and Japan.
So, I count out what I want to keep for my own games and put the rest on eBay. Sometimes I might lump all the extras in a big lot or make up a bunch of little sets. There are guys out there that are even worse piece junkies than I am and my game pieces pretty much always sell.
As for the extra game boards, instruction books, cardboard accessories and dice, you can put them on eBay as well. Some guys out there have a lot of playing pieces but perhaps missed out on whatever game you are offering, or just don’t want to go out and buy a new one. I found the best way to ship these, especially with the game board, is to use a USPS Large Game Board Flat Rate Box. You can put all the game accessories in one of these along with some packing material to fill in the extra space and the USPS will ship it anywhere as long as it doesn’t weigh over 70 pounds. For shipping within the US, I think it costs $16.95. You should check usps.com to be sure. I don’t know about international shipping because I only ship within the US.
The MOST important part is to price these items to sell. Start low and take the shipping cost into account. If you start out with too high a price, you won’t get any bids and will be stuck with them. Even if your starting price isn’t too high, remember they will have to also pay shipping. So start low. You are probably not going to get what you paid. The object here is to at least make a little money back on your investment and provide some gaming materials to someone that can use them. Even if you just get the lowest bid, at least you get that amount for yourself and you get rid of the excess pieces.
Another option is to offer free shipping which can draw more looks at your items, but then you have to either start your bidding price to include the shipping costs or take a loss with the shipping charges.
Good luck.