I'm going to start off with something very obvious. Arkinventory has got to be the easiest and neatest bag mod to use in the entire game. I have mine currently resized to fit every item in my bags into a space that would only be taken up by a single bag, and I have very big bags. You can even set options in it to organize your entire bag for you (though I haven't jumped into that aspect of the mod, I tend to organize the bags myself.)
Overall it's a very nice, neat way to keep your bags organized and taking up very little of your screen.