Well, you can't technically be charged for possession since you aren't in possession of it. Technically its in your wallet which ties the meth to you, but as 'army judge' pointed out you can deny it's yours or know where it came from.
Although it certainly looks bad on you, criminal charges would be hard to support. If you are approached by police do not make any statements or claims on the wallet. Let your attorney know so he/she can be prepared.