in the end, you'll see that crap can accumulate, aand weight, and it will shock you riding that bike first time with all your junk on it and how bloody slow it is to accelerate and hump up hills, even small hills....
Its pretty common to take too much junk first times, and if you havent done self propelled outdoor activities before, youll most likely pack too much
but live and learn, a mini u lock is pretty darn heavy still. but it depends on many factors. Ive just never taken one myself.