As I have some favorites I also have some products that haven't worked so well for me.
1.) Any snack container that was "spill proof".
If it was meant to trap food in while letting your kid get food out I tried it and my daughter found a way to prove the claims wrong. The flaps they put on the lids bothered her. She didn't like the way they felt. But she still wanted the food. She would start by shaking it and food would fly out if she shook hard enough or at the right angle. If that didn't work or wasn't fast enough, she would work on prying off the lid.
Let's assume my daughter is just your average monkey of a kid (not the genius I assume she is). If one kid trying these stack containers out between 10-24 months can do this, I would think there are others out there that can too. So for $3-$10 that it costs for one of these "magic" containers, its not worth it.
I got some cute flip top ones from the dollar store and they have worked best because they are easy to get into and easy to close, and I really don't care if they get scratched or dented because they are only $1.
Sadly, I haven't given up the search for the perfect teether. So far though, everything I have tried has not served its purpose. Anything specifically meant to be used to chew, gnaw, and drool on, held no interest for my daughter. She would much rather go after board books, soft training spoons, hair brush handles, medicine droppers (the rubber part), blankets, other toys, and so on.
My 4 month old son is now teething and I have excitedly brought out all the paraphernalia I could find and I have even added to the collection. I have not given up hope that these will all work for him, but the realistic side of me knows he will probably end up chewing on one of his sisters dolls or on some random household object rather than the wonderfully designed, BPA free thingamabobs that were purchased for the sole purpose of relieving his teething discomfort.
3.) The Infant Car Seat/Carrier
This one isn't really the product's fault at all. I actually love my seat and the stroller it came with. The problem is one of genetics. My kids have been above average in size from day 1. My daughter was born at 8 pounds 13 ounces and my son was 9 pounds 3 ounces. At that point they already didn't fit in newborn sized clothing and newborn diapers lasted a week. So the infant car seat that we got with our travel system is supposed to last the baby's first year (in theory anyway.) The weight limit is 22 lbs and the height limit is 30 inches. My daughter was 20 lbs at 6 months and my son is on his way to meeting or beating that weight by then. So we had to invest in a convertable seat for my daughter at around 5 months when their was a sale. We just did the same for our 4 month old in anticipation of having to change his seat soon.
As for the "carrier" feature. Yeah right, is all I have to say. Those seats weigh about 8-10 pounds on their own. Sticking an 8-10 pound baby in with it made it ridiculous to carry. It got worse when both kids were 15 lbs by 2 months old. I, for one, am not fond of lugging around almost 25 lbs of awkward weight with a packed diaper bag and a 2 year old in tow.
The good news is about a year after we bought our system companies started making seats with higher limits, but the carrier will still not be convenient what-so-ever if you have a big, heavy baby. Keep that in mind before spending $200-$300 on a travel system. You will have to invest in a convertible seat that will last up to 65 lbs at some point and it would be good to have a baby carrier like an Ergo or a Beco Butterfly II, which will both last through about 2 years or 35 lbs.