In reply to JAO89:
We didn't really get anything special (edit: beyond the basics, ie a couple of waterproof oversuits, hats, mittens etc), we just layered him up a lot. To be honest, by the time he was a bit gone one we figured that he wasn't really having much fun just being toted around the place so we needed to plan activities more around having him running around rather than sitting in a backpack / bike seat for extended periods of time (although we did still use the bike to get him around the place...)
One thing I would recommend if she's not walking yet are waterproof foot-bags, like these:
https://www.waterproofworld.co.uk/accessories/celavi_booties.htm
They're cheap, durable, warm, as waterproof as anything that you can get a foot inside and they stay on fairly well. Really good for playground sessions in dubious weather.
Post edited at 10:33