Heat a nail or large screw while using pliers ore Vise-Grips to hold it and MELT a hole through the bottom near the side. It makes the container stronger - much less likely to fail due to a break-out from a weak hole.
I use a lot of old prescription pill containers for rooting cuttings. I keep a cheap soldering gun handy on the work bench & just poke holes in the bottom as I need them. It's amazing how often I want a hole in something plastic so I can anchor a branch or plant to it or push a wick through it to help drain excess water from the soil.
The dollar store is a great place to look for gardening supplies. For a while there I was buying plastic trays that held 12 / 4" pots perfectly from there. I was crushed when they stopped carrying them, but I see they have them back this year, yipee. They also have lots of good plastic bowls and such to use for tufa or cement pot molds!