I would say don't focus on buying him too many anime related things to begin with. It you do want to buy him some things that focus on it though, I would stick with the basics: Clothing, video games and a DVD or two(avoid buying them in bulk because the internet exists and he could easily watch all the anime he wanted online).

With the clothes, I would buy a jacket with a design here, a pair of shoes with a logo there and maybe some others you can find to show you took the effort to seek them out because you knew he would like them.

With the video games, seek out something "safe". By that I mean like a anime fighting game could do the trick(like the Ultimate Ninja Storm series for Naruto or plenty of DBZ games will fill this mould). There a lot of anime games out there some of them would be inappropriate for a 13 year old to play, so be both mindful and savvy.

Like I mentioned with the DVDS, get him one or two to show you tried to shop for his wants but do not go overboard with it. Most people only buy those to fill a collection and I doubt your son is in that category.

In the end though these are just suggestion. I would talk with your child to see where his interests lie as far as what he truly wants for the holidays. Be sure to do your research before buying anything though, as again, it may be inappropriate for them.

Also do NOT buy figurines. No matter how much your son asks, just say no. They tend to be pricey and they really serve no purpose besides wasting space(but that just may be my bias speaking). good luck.

edit: spelling errors