What are the snacks? Can you use the recipes you already use?
You can calculate calories per portion by taking the nutritional info for all the ingredients in your recipe. This is sort of a pain but you only have to do it once. There are nutritional info calculators online you can plug the ingredients into.
Once you've figured out how many cals are in the entire recipe, then make the recipe. No snacking or snitching on the dough or any of the results till after you weigh THE ENTIRE BATCH. Once you know the yield, then divide the total calories by the number of ounces to get the calories in one ounce. From that, multiply the number of ounces it takes to get 100 calories. Package that amount in Ziploc snack bags, then put the small bags into a larger bag and store in the freezer to keep things fresh.
Write down your recipe and include the nutritional info plus calories per ounce and/or ounces per 100 calorie serving on the recipe, so you don't have to calculate things again. Then when you make the recipe again, you'll just have to weigh the correct number of ounces and package them up.
You can do that with any recipe.
If you're doing things like chocolate chip cookies, then of course you will need to make them small, and for that reason, use mini chips instead of regular chocolate chips.