Most nappy bags do not complement babywearing well. Backpacks or wide adjustable strapped messenger style bags do work - backpacks provide a better centre of gravity when carrying on your front but are awkward if you want to carry your child on your back.

There is a bag called the onbag (made by a UK WAHM) which is specifically designed for babywearing. It has wrap style straps that can be tied in a few different ways, depending on how you are carrying your baby. They aren't that easy to get though, although if you sew, the pattern is available for non-commercial use.

I've also heard a few people say really good things about the bags made by the WAHM who does Nice Knickers on Ozebaby.

I've used the OiOi hobo bag quite successfully with mei-tais and wraps, I also have an Isoki bag which is wonderful but I wouldn't carry it (with or without a baby in a carrier) for any extended period of time without a prior appointment with my chiropractor. It is not a good 'carrying' bag LOL, but it does fit the kitchen sink.

I also know quite a few babywearers who swear by granny carts (you know the pull-along shopping cart thingis that are favoured by market going grannies).

HTH!