On a flight the luggage compartment is at cabin pressure. If it wasn't then the pets in the hold would suffocate.
Glass bottles are very strong. Plastic ones are strong and shatterproof.
Do you really not have pints down there in the USA? Nothing like this?
There are such small bottles for sale but the selection of those down here tend to be limited to more generic stuff I believe...
Yes, around here those small plastic bottles are expensive and generally pretty generic low-end stuff. $6 for 3/4oz of low-grade liquor isn't a good option for me. Now if I could find a 200ml or 375ml in a reputable brand, I'd probably give one of those plastic bottles a "test drive".
On the flip side, most of the plastics I have been around really hung on to flavors so, I'd also have to dedicate each bottle to a single liquor type. Being a good "solvent", they penetrate a lot of plastics really well rendering them pretty useless in the long run.
Thinking this through some more, it may be worthwhile to just travel the ~2 hours each way to Dallas and hit the local liquor stores for small thinnish glass bottles and give it a go. Maybe I can score some 375ml glass rectangular bottles to play with.