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I also plan for a nightly snack, as long as it falls between my daily calorie range. The most filling snack for me is popcorn. I currently use Jolly Time butter-flavored micro popcorn (3-bags per box). This popcorn is Weight Watchers approved as well. One bag will make up to 5-cups of popped corn, with only 110 total calories.
If you like potato chips, you might try PopChips...a potato chip which is popped like popcorn, instead of fried or baked. One 28-gram serving (about 23-chips) is only 120-calories, and is low in sodium. They are surprisingly good and satisfies my taste for chips.
Raisins are another good option. Sometime I like to eat 1/4-cup (120-calories); raisins are quite healthy for you as well.
And then there are almonds. I buy honey-roasted almonds. A 1/4-cup (30-grams) are 170-calories. I eat them one at a time while watching tv. Nuts are quite healthy for you as well, although if you eat too many of them, you will consume a lot of calories.