Which electronic materials r those ?
Any thing that can be consider hate literature and that depend on the countries you might be visiting. In some areas of the world the Christian bible can get you in trouble as I said it all depend on the area of the world you are visiting.
Off hand for myself a few issues of the middle east terrorist E magazine Inspire and a far right racist/neo-Nazis book call the Turner Diary in book format.
Both Canada and the EU could give you problems for having either materials on your computer/ebook reader.
Strange reading in both cases but still interesting for anyone who would like to try to understand the thinking of either group.
However people have ended up in prison for having such materials on their computers in such so call free countries as England even in the cases where the court had acknowledge that the person who had it had no criminal intend but have it for research purposes only.
We Americans can be thankful that ideas even ideas that are sickening/hateful can be examine without fear of us going to prison for looking at them.