modern lights +1
tire & tube improvements +1
laprade +1
foam rubber bar tape
modern padded saddles ( I tried a Brooks Professional for a couple of years in the old days; neither of us got 'broken in' to the other to the point of my being comfortable )

I use the above gladly, but I was getting along fine (except for the saddle) before they came along. Pretty much everything else on my rides is "old school", except racks & bags, which aren't revolutionarily different from the old days.