Always carry two large band aids in your bag. Let's all admit, when we really get into our photography we sometimes take risks we shouldn't take and which lends itself to scraps and bruises. And we’re usually no where near a drug store. Aside from being used for wounds, band aids are great if you need some tape. Let's say you drop your point and shoot camera (because heaven knows a “real” photographer we would never drop our DSLR!) and the battery door is broken and won’t stay shut. Just pull out your band aid and tape it! So why two band aids? Because whatever you did to break your camera means that you'll probably need one for yourself too! [Be sure to replace these once a year, band aids do go bad]
Now that’s a cheap trick!