Hi there - Im an ebay whore from years back.
Last time i stayed in Taiwan I sent 8 - 10 boxes full of weird junk back home to sell later on ebay. I found that unusual, quirky things sold really well. For example, back in 2003 some 7-11s were selling cheap LCD games called ‘OSAMA vs USA’ or something… It was basically a boxing game, but the artwork was hilarious.
These cost me about $9 AU and I sold them for up to $60 AU each.
Another tip - find something that you LOVE and specialise in those items. I am a big video game freak from way back, so scoured a lot of smaller video game shops for unusual game accessories, games and novelty items.
I hit the jackpot in a delapidated gaming store in Ching Shwuei(?) in Taichung. Found a whole carton of 1990s game accessories which I bought for a few hundred TWD and a mint condition ‘Knight Rider’ remote control car from the 1980s. That item alone paid for a weekend in a hot spring resort 
So - find something unusual that nobody else is selling, and concentrate on stuff that you have a passion for and generally enjoy hunting around for.
May I suggest memory cards for mobile phones/cameras? These tend to be cheap in Taipei and are small and light (an important consideration)
Good Luck!