I think you need to be careful about purchasing the shakes, bars, etc. that some weight loss programs suggest - they can be expensive, and they are teaching you to substitute their product for what you are eating rather than teach you a long-term, sustainable solution to make better choices. In general, I'd prefer an approach in which you buy and prepare your own food.
I have tried several different programs before, including weight watchers, Nutrisystem etc where I bought their foods. None of it worked for me. What worked for me was learning to make my own foods. And the biggest helpful tool was a food diary. I ate like normal for a day or two and tracked everything, I had no idea how badly my eating habits were. Then I started preparing my own healthy meals, I would make 3-4 days worth of food and put some in the freezer and I would label the containers with nutrional content to make counting easier. After a while I didnt need to continue coutning because I knew how much was what. I dont think I can go back to prepackaged, prepared food. It doesnt have the same quality as fresh foods.
If you go with Weight watchers they do want you to eat their stuff. It's money for them and it is supposed to makes it easier to you to count up how many points you have. At least until you learn the correct portion sizes via eye, and you get used to eating how much you're supposed to. However, a lot of weight watcher programs can be a community based meeting points. These can be good or bad depending on the group- a lot of people whining vs positive we can do this. So if accountability is what you're after, then this could work for you. See if your work sponsors a weight watchers meeting; this is usually more cost effective than doing it alone.
I know with Jenny Craig, which is what my husband successfully used to loose 25lbs, they told me it was pointless for me to sign up. One on one meetings with them might be nice but I have so many food allergies and requirements I can't eat any of their food. They usually make you buy their food for several weeks then slowly put your own in. Again the idea is -this is what you should be eating in these amounts, now you try to make it all yourself.
As far as those snacks go beware!! Those 100 calorie snacks are so easy to eat several of and then it's no longer 100 calories you're eating. If you have a severe sweet tooth and aren't comfortable with your will power, best to stay away from them entirely. Personally, I opt for a piece of fruit instead of something like a cookie. I still get my 100 calorie snack +/- but it has a lot more substance and vitamins in it. Plus none of those additive junks your body really doesn't need. For desert I bought some popsickle forms and put pureed fruit inside it. They hold about 1/2 a serve of fruit and if you use something like mango they're a sweet and tangy dessert. I'm not saying they're all junk and will ruin a diet- but you have to be very cautious because they're small, not filling, and easy to eat multiple of.