Since Mod Podge is used for so much, its pretty easy to run out of.
YouTuber Jennylove217 makes her Mod Podge with 2 parts glue and 1 part water.
For the amount she makes, get two bottles of regular school glue.

Pour both into your container of choice, just double-check it has a lid.
Next, fill one of the school glue bottles with water, and pour that into your mixture.
Seal your container and shake well.
Watch Jennys tutorial below and give it a shot next time you run out!