I'm curious as to what easy advances there were in cooking. Do you mean something along the lines of better heat sources or do you mean recipes?
- Pasta? Pasta is absolutely amazing. It is an extremely dense source of calories, which doesn't rot, is super-compact, and only requires water and heat to cook. Great for armies on the march.
- Coffee? Coffee's been around a long time, but high-pressure espresso is relatively new.
Other fairly basic staples are newer than you might think, like Potatoes (16th Cent.), Or Tomatoes (17th Cent.)
Edit: Also limes for sailors.
Also without fortifying the flour pasta is calories without nutrients. It's useful as a suplement, but dangerous to live on it long term.
I don't actually know if you can or not, I was just wondering.
http://en.wikipedia.org/wiki/Whole_wheat_flour
Grind whole wheat into flour with a coffee grinder: http://www.associatedcontent.com/article/1593906/make_lowcar... (you can also buy an expensive hand-crank version)
Whole Wheat Pasta recipe: http://www.sugarlaws.com/whole-wheat-pasta
Actually that's a terrible idea. You want lemons, not limes. Really.
See http://idlewords.com/2010/03/scott_and_scurvy.htm for a discussion of where the myth to the contrary came from, and for the complex history of how the proper prevention of scurvy was discovered, forgotten, proved false, and only later rediscovered again. It also discusses why you really don't want to use limes.
For example: how do you avoid drinking alcohol if your only sources of drinking water are contaminated? You can boil the water — but you don't know a priori whether the pathogens or toxins in the water can be destroyed by boiling, or how much boiling is needed. If the toxins are things like arsenic, boiling the water will concentrate them, while various kinds of biological processing may filter them out.
And where do you get vitamin C? Tomatoes are a great source of vitamin C, but you can't just go around eating random local tomato-like plants; almost all of them are deadly. Plants like rhubarb have lots of vitamin C, but also lots of oxalic acid. Raw meat is also a good source of vitamin C, but raw meat can harbor many different pathogens. Are you going to build a microscope, synthesize some stains, and inspect a bunch of meat samples to see which ones bear pathogenic bacteria?
And once a couple of your human-subjects experiments go wrong, or just have coincidental unrelated deaths, you're a candidate for a witch-burning.
(Even in the best cases, modern hygiene is not without its drawbacks; the poliomyelitis epidemic is one example.)