I have an idea to make liquid oxygen at home, but without any calculations, I am not sure whether it will work at all. The idea is based on the fact that gases tend to liquefy easily in higher pressures.
So here is what I plan to do:
Get a soda bottle, and install a bicycle valve on the cap.
Pressurize the bottle using a bicycle pump as much as possible.
Put the bottle in the freezer.
Take out the bottle from the freezer, and pump in more air because keeping the bottle in the fridge would have lowered its pressure.
Repeat a few cycles until no more air can be pumped in, without increasing the pressure excessively.
Finally, release the valve. Some liquid gases should have formed in the bottle.