In a desktop app I usually have a modGlobals module which I put Globals, which, as I understand, wont work in a web app because all multiple users may have access to that area.
If I put global in the Session area will be ok as each user get thier own.
I agree with Michel as this is safest, but if these variables NEVER change for ANY user or are constants, then placing them in modGlobals or app is OK too.