Proper town bikes, like mine, have a rack and panniers. Panniers which are full of stuff.
Often this comes in handy. We live in an area prone to power cuts, and quick access to bike lights has often helped us through the darkness. I can now make beans on toast illuminated only by a back light in flashing mode. Well, you have to save power. These cuts can last a while. It's like a disco version of Ready, Steady Cook.
The most useful things in my pannier however are not the lights. Not the waterproofs either, not even after the storm we cycled home in last night and filled our street with hail the size of cherry stones. Not the tools, not the Swiss Army knife whose only bits I ever use are the scissors and corkscrew, not the 10x optical zoom digital camera. Not even the occasional bottle of wine just in case I get stuck in the roadworks currently by Waterloo.
Nope: the most important ingredient of any town-bike pannier is the Emergency Chocolate. Not for you, of course - you're unlikely to get The Bonk in a two-mile wobble home from Wetherspoon's - but for your colleagues. (Obviously I wouldn't wish to be unintentionally sexist, but you'll guess there's something gender-specific about this.)
It's remarkable just how often my pannier stocks of cocoa-based confectionery bring instant relief to stressed people at work, on the train, at concerts, in lectures, under the cosh of family gatherings... even, once, memorably, a bewildered but instantly grateful stranger on a bike at the lights. Well, I thought she must be in need of a dose of Green & Black's by the way she'd shouted at a stationary taxi for cutting her up.
But a warning: if you do transport slabs of Lindt 80 per cent round in your pannier, do make sure it's well wrapped up. Especially in a heatwave. Scraping congealed chocolate off your laptop and library books is laborious, and it doesn't taste the same afterwards.