Would you bother preparing something to help prove your reincarnation, or would you simply take advantage of whatever you retained (and prepared for yourself) from your past life?
How might you use this ability to help yourself and others?
Edit:
To clarify, suppose you have some vague memory of your past life in your reincarnated self that helps you along and allows you to take advantage of whatever your past self prepared for you.
A Trust Fund that has accrued at least 80 years of compounding interest. I will have the estate to only be released to a person (my reincarnated self) who knows the secret password after reaching 20 years old.