Skiing is expensive. Single-day lift tickets are inching closer to $100, but that's a drop in the bucket. Try adding in the cost of lodging, food, travel, and equipment (rental or otherwise). Finally, put some value on your time spent driving, away from work, and generally not doing what you normally do. Skiing is expensive.
It's OK to spend some money to have fun. The real tragedy would be spending all that time and money and then wasting it. To avoid that, I suggest working on the Five L's:
Fix this problem in the month or so leading up to the ski trip. Legs can be strengthened various ways. I'm fond of wall sits, lateral jumps, and running. Two hours a week can make a huge difference. At the risk of cliche: strong legs are the foundation upon which all the skiing happens.
On the subject of legs, don't forget comfort. If your toes are numb, calves are cramped, or your shins are just killing you, how are you going to ski well or enjoy it? The smart money's on a pair of dedicated ski socks, as from Eurosock, Thorlo, SmartWool etc. Medium or heavy socks are usually for rental boots. For your own boots, use thin socks and do the boot fitting with those socks.
If you're a renter, but you've got some dough, consider buying boots. While it's possible to rent perfectly fine skis and poles, nothing can beat your own pair of custom-fitted boots. The boot is the one piece of equipment that must conform to your unique anatomy. One warning, however: only buy boots that really fit well from someone who knows how to fit ski boots. Don't ask how I know.
Solve this problem similarly to the legs. Do aerobic exercise in advance. Many things will work. Running, swimming, cycling etc. are obvious choices. A number of activities will help both the lungs and the legs at once. I suggest exercise that mimics the intensity profile of skiing. Rather than a long, slow run, alternate sprinting with jogging, with some hills thrown in. You can train for sitting on the lift afterward.
The obvious path here is to take some lessons. Almost every mountain has many levels of group and private lessons. Most people report the money's well spent. Lessons can also be had from friends if you're lucky enough to know the right people. Some people also learn well from books. There are a number of well-reviewed books that illustrate and break down techniques so they can be understood, imagined and practiced. Finally, try reading online skiing forums.
Learning may not be the whole story. Practice counts for a lot, too. Perhaps you've heard of the 10,000 hour rule. Research shows a strong link between time spent practicing and excellence. After all, you ski with your body, not just your brain. Knowing what to do is just the beginning.
On a related note, be aware of what happens when one stays up too late, especially if one is drinking alcohol, and one is at altitude. Many people I know go to bed unusually early in the mountains.
Consider making sandwiches in the morning and putting them in ziploc bags in pockets or backpacks. Around noon, break them out on the chairlift. Of course, you're free to eat anywhere you choose, taking as much or as little rest as you desire.