As far as the walk is concerned, I don't think it will be possible, although so far this year I can't say for sure. I live in Wisconsin, and although the temperature is usually -39598 degrees at this point in the year, it is still around 80 today. However, I would expect by then it will be ridiculously cold, and a walk probably won't be the best option.
I agree with you on the ring in the food thing as well - I think it would be fine if it all worked out, but knowing my luck my bride to be would end up choking to death before I got an answer out of her.
Ideally, we'll be able to stay at a hotel that night - for her birthday last year I rented some ridiculous suite with a hottub/whirlpool in it, and it was quite fun. However, that will probably depend on what I can arrange for her work - if I can't get her off, then it'll probably be a no go.
I'd be interested in seeing how most people feel about where they are proposed to - whether it would be better in public or private. Maybe I can persuade one of the TFP's lovely ladies to put a poll up in the ladies lounge.
Thanks for the ideas folks - and keep them coming