- Use a laser printer if you can instead of an inkjet, and laminate the paper as already mentioned.
- Be sure that the word "bitcoin" is nowhere to be seen, you don't want someone who stumbles upon your treasure to know what they've found.
- Be sure to seal the space between the jar and the lid with wax.
- Don't use a metal lid, if you do, the seal it entirely.
- Put a plastic bag around the jar and seal it tight.
Of course one could go on and on
Good luck, Mr. future millionaire. I found a picture of you in 50 years.