I'm planning on carrying my Canon 7D with a Canon 50mm f/1.8 II lens to an event but have to walk through some light rain (~15mins). Will the camera and lens be fine?
The Canon 7D has quite nice weather sealing - "Canon considers the weather resistance of the EOS 7D to be slightly better than the EOS 5D Mark II and 50D cameras, but not as robust as the EOS-1D series." (Chuck Westfall, Canon USA)
What this basically means is that you can not worry about shooting in rain. I wouldn't take it swimming, but you might be able to get away with a dunk in a pool.
The 50mm f/1.8 on the other hand, has essentially no weather sealing. It is almost all plastic, and has no seals or gaskets to keep water out. In my personal opinion, it is such an inexpensive lens, I wouldn't worry about it much. I wouldn't want water to enter into the lens, then into the body of the camera though, so don't get it too wet. This lens is not "resistant" at all. It is more like a sponge :)
So to sum up, unless you are really worried about the very inexpensive lens, I would just shoot away as normal. If you are really worried, I would either upgrade to a weather sealed lens(and filter if necessary) or do what I do when shooting without a weather sealed kit - just leave it under my jacket until I take a shot, then wipe it off a bit before putting it back away.
7d's weather sealing is as good as the lens attached to it. 50mm f/1.8 is not weather sealed. 7d has been known to resist mild water splashes, however there is no empirical data to support that claim. This question digs a bit deeper into the weather resistance of 7d.
I know you asked about the 1.8, but I have 50mm f/1.4 with the 7D, and I HAVE shot in light rain with it, and it's been fine. Though by that I mean it did get raindrops on it but I was careful not to expose it too much to the elements. The 1.4 and 1.8 fifty's are not weather sealed like the 7D is!
That said I would recommend a UV filter on the front of the lens. This helps prevent any water from entering through the front of the lens, and is an inexpensive way to protect the front of your glass anyway.
DISCLAIMER, just because it was fine for me don't take as gospel that it will be fine for you. Judge the conditions, take care with your kit, and don't let the lens get too wet. Wipe with a dry cloth immediately after use.