Having reviewed the evidence that a tiny bit of glucose goes a long way to improving your mood, and bearing in mind that low-carb diets eventually test the will of people with a sweet tooth, here is a quick list of some snacks that, when eaten sparingly, provide a nice pick-me-up without being too sweet. If something tastes very sweet, even if it lacks sugar, the mere taste will trigger the insulin response, so don't think that dumping a bunch of Splenda into something or wolfing down 10 sugar-free Hershey bars will bypass the process.
1) Turtle Mountain's Purely Decadent ice cream made from coconut milk. You'll probably have to go to Whole Foods to find it. Coconut milk is almost all fat, and its fat content boasts a higher percentage of saturated fats than butter, lard, or tallow. Since Turtle Mountain caters to yuppies, they have to remove quite a bit of the fat, so it's not quite as rich as Haagen Dazs or whatever, but it's still pretty thick and smooth compared to soy and rice ice creams. Has about 13 g of sugar and 21 g of carbs per quarter of a container, but I only eat about 4 spoonfuls.
I've been lactose intolerant since I was about 23, and this is the closest thing to real ice cream I've had -- it could do a lot better, though, by leaving all of the fat in, which would also allow them to remove some of the carbs. So far I've tried Mocha Almond Fudge, Chocolate Peanut Butter Swirl, and Passionate Mango. All great. Again, just take a little after a big meal.
2) Dark chocolate and peanut butter -- I could never give this combination up, but now I need to find a low-sugar form of it. Lindt makes an 85% cocoa bar that has only 5 g sugar and 8 g carbs per serving, and lots of saturated fat. The other dark varieties, whether higher or lower in cocoa, have higher sugar and/or carbs (obviously stay away from milk and white chocolate, which are full of sugar). It's not bitter at all, but it does have a very strong dark taste.
Finding peanut butter without a lot of harmful polyunsaturated fats is tough, but Smart Balance peanut butters have very low levels, and they're at least pretty balanced between good omega-3 and bad omega-6 polyunsaturated fats. Has a ton of monounsaturated fat, as much saturated fat as a portion of ham, hardly any sugar, and few carbs. It's not quite as savory as hazelnut butter, but this brand is much less sweet than all other peanut butters I've had.
Just slather a big hunk of the peanut butter on top of the chocolate, and take it with some low-sugar soy milk or honey bush tea, to add some sweetness. This is easily one of the richest things I've ever had -- all that fat pumped me so full of energy that I couldn't sit still and had to work it out by dancing around vigorously for about an hour. If you've ever wanted dancer's legs, having one of these a day will make it happen.
3) Blackberry or raspberry smoothie made from coconut milk. In a blender, mix a full can of coconut milk -- not the low-fat or lite kind -- enough soy milk to thin it out a little (maybe a cup or two), two packets of Splenda, and a container of blackberries or raspberries, which don't have much sugar. Remember, coconut milk is fatter than lard, so don't drink a tall glass of this stuff -- a cup or a cup and a half is plenty. If you can have lactose, use full-fat animal milk and/or full-fat, unsweetened yoghurt instead of soy milk. (It's the lesser of two evils for me -- it has some polyunsaturated fats, but has much lower carbs than rice or almond milk.)
All of this stuff is gluten-free, too. Once I found out I couldn't have gluten, it was pretty hard to find snacks -- and most of the gluten-free cookies or whatever taste incredibly bland and are high in carbs anyway. Stick with the above, and you can't go wrong.