很多人都会攒一笔钱，以备不时之需。在英语中，我们用a nest egg “一颗窝里的蛋”特指为将来某种用途存下的备用的钱。
例句
I want to build up a nest egg for my retirement so I always save whatever I can every month.
Without our nest egg I don't know how we would have been able to afford to get the roof fixed.
I've got some money set aside as a nest egg, in case of emergency.
请注意
另一个和鸡蛋有关的表达put all your eggs in one basket “把所有的鸡蛋都放到一个篮子里”的意思是将一切希望或钱财都寄托在一个项目或计划上，孤注一掷。一旦篮子倒下，鸡蛋将会全被打破，一切则付诸东流。我们常用这个习语警示人们不要为某一件事冒险。
例句
Don't invest all your money in one company. It's never a good idea to put all your eggs in one basket. What would you do if the company crashed?
I get a lot of work form this company, but I don't want to put all my eggs in one basket so I'm taking time off to look for work elsewhere.