I am a 31(?) year old auto mechanic, and I have about a dozen of them.
Buy the damn messenger bag, it will last your entire life, and you will be amazed how much you use it.
Later in life, buy more bags. Overnight duffles, carry-ons, shaving bags, real luggage, brief-cases...
Just buy good stuff, add them one at a time as you can, and they will last forever.