Thought I'd share some tips that I've learned or heard.
Celery - to keep celery crisp for weeks, wrap it completely in foil. (This works!)
Beaten egg whites - add a pinch (1/8 tsp) of cream of tartar to your egg whites when you beat them. This will prevent your beaten egg whites from flattening/collapsing when you fold them into your batter. (Haven't tried it but heard it from Giada on Everyday Italian.)
Cakes - to prevent your cake from sinking in the middle while it's baking, make sure you cream your butter and sugars well. Also make sure your batter is mixed well. (This I just learned recently from experience. I was too afraid of overmixing my batter that I wasn't mixing it long enough. Don't know what I was thinking! LOL)
That's all that I can think of right now.
What are some of your tips (tried or rumor)?