Micromedex does not list any precautions or patient educations notes for Dexedrine and caffeine. However both substances can have an effect on heart rate and blood pressure. Large amounts of caffeine like energy drinks or espresso would be ill advised, but I wouldn't think the small amount in a pop would have significant effects especially if you're decently ...
Yes, unfortunately, Ritalin produces a tolerance in individuals who take it.
In the conclusion of this double blind trial, the author notes,
Acute tolerance to methylphenidate appears to exist. This should be
considered in the design of an optimal dosing regimen for the
treatment of children with attention deficit hyperactivity disorder.