Yeah I totally thought this thread was going to be about soda bottles for babies. Which would not have surprised me one bit.

Your mention of BOB didn't help either as that's the name of a super sexy baby stroller.

The site says:
"Measures 15 cm (5.75") tall, 2.5 cm (1") in diameter and holds approximately 60 mL (2 ounces) of liquid" for those interested in specs.
At 2 ounces, they seem ideal or least suitable for some uses. They seem durable and light enough. At this size you could improve in weight and the quality of the plastic.

I wonder how strong they are. Can I break them with my hands if I try?

I can see the use of these for tiny part storage, or for anyone traveling/camping with paper documents you can roll up and keep dry.

I want some just to play with, but I really can't think of a practical use for my daily life.

These would be good for packing rubbing alhcohol, peroxide, iodine, etc. for a brigade level first aid kit.

I have a friend that works in a Soda plant, these are bottles before they are made into 2L size, and as far as BOB its funny because we always use these when we go in the woods to bring sugar, milk, etc for coffee and tea

Very heavy duty item. I had a few back when plastic 2 liter bottles were a new thing and had metal caps. If you can break one with your bare hands, I am not going to mess with you.