Save that same amount of cash in an investment of your choosing.
Ordinarily, I'd be right there with you. But, right now, short-term investments (<= 1 year) have such lousy return rates (or, such high beta values) that it's hardly worth bothering.
But, the broader point is well taken. I once asked my doctor about whether or not low-carb this or atkins-that was worth thinking about. He stopped, looked at me, and said: "You understand basic physics. There are no secrets to losing weight. You have to burn more calories than you take in."
Saving for trips is like that: you have to spend less than you earn, week to week, month to month, to be able to take vacations.
We do that primarily by accepting that
things don't lead to happiness, experiences do. We still have a few pieces of "grad student furniture" even now in our mid-40s. Our kids are the only ones they know who don't have the latest (or even the not-quite-latest) video game system. We buy a car, and then drive it into the ground---a process that takes a good 12-15 years, rust and all. Our home's interior is not at all
au courant---several rooms are still clearly mired in the late-80s, though over the past ten years we've lived here, we've slowly painted over the worst of it. The few home improvements we've done have been about experiences. For example, we finally dumped the hot tub that was here when we bought the house---a feature we never used---to be replaced by a larger deck and patio/fire ring, something we use all the time.
Some other things prior folks have mentioned that are important: pay yourself first, every paycheck. Part of it to savings for college, retirement, etc., and part of it to your "fun fund." For example, I work a side job from time to time, and for money earned there, my allocation is simple: 1/3 to taxes, 1/3 to savings, 1/3 for fun. Get in the habit of paying off your credit cards in full every month, and do the best you can to eliminate consumer debt.