The answer, of course, is "it depends". What's your commute like, and what's the "absolute BARE minimum" of stuff that you need to transport back and forth? For me, with my commute, a lock is necessary, a tube and pump are not (I commute in a city, public transit is always there if I have a flat, but if I have to stop I need to be able to lock my bike). I don't need a rack or trunk bag or panniers because I use a backpack, which is also what I use when I'm not on the bike -- one bag goes everywhere. So...it depends.