Buying single-size servings of snacks (such as 1 oz. packets of peanuts, a favorite of mine) makes book-keeping much easier, but they are more expensive than buying bulk foods, and of course, you can't use that method for your own creations.
So, what I do is very simple. I get the "snack size" zip-top bags, portion the snack item into the bags, zip them closed (removing as much air as possible), and then use a permanent marker to write the carb count for the portion size on the bag. (If you're making up a whole bunch in advance, putting the date on there might not be a bad idea.)
It solves two problems for me -- 1) the portion control issue of knowing how much I'm having at one time, and 2) somewhat related, what I call the "open container syndrome", which is the tendency of finishing off a container of something once the package is opened. Tackling the mental issues with the physical ones at the same time is what makes this tip really useful.