Reddit mentions of Zefal Air Profil Fc02 Mini Pump - Black/Red, Small

If you're planning on doing more than just a short commute, you'll want to get:

• Some padded shorts. Bib shorts are the best as they don't have a waistband to dig into you, but you could get 'baggies' if lycra is not your thing. I use these but I'm not over impressed with the quality, though they are inexpensive compared to most.
  
• Some cycling gloves. They'll stop wind chill, stop you grazing your hands if you fall and reduce hand numbness. Typically people use fingerless ones for the summer and fingered ones for the winter.
  
• Water bottle. I use these ones as they're dirt cheap and big.
  
• Pump. I quite like this one.
  
• Spare inner tube. I bought my last batch from Ribble.
  
• Patch repair kit. I tend to get cheap ones from Wilkinsons.
  
• Tyre levers. I have both plastic and metal ones and the plastic ones are better.
  
• Multitool. I use a cheap one I got from Sainsbury's.
  
• Saddle bag (for carrying the spare tube, mulitool and patch kit). I use this one and I'm pretty pleased with it.
  
  That's the bare minimum, I'd say. You can ride with less but it'll be less comfortable and more inconvenient when you get a puncture. You'll also need lights if you ride at night, of course. A proper cycling jersey is also really nice and a massive improvement over a t-shirt but you don't need it.