I dont think there is any dress code just whatever you are comfortable in and something suitable to wear to a church. You may have got something by now but I was at a christening on Easter Sunday. You of course have your regular church goers there wearing whatever they fancied (some very casual) but with regards to the christening party it was quite mixed. I wore a kinda smart but fine t shirt material dress with some sandals and my friend wore just a summer skirt, t shirt and some pumps. On the other hand some of the party could have been over dressed at a wedding!! Enjoy!