Avoiding being wiped out after work commute?
The simplest advice is: just keep it up. Give your body time to adapt to the new workload you're putting on it, and it will get easier and easier.

For drinks, you can buy gatorade powder and mix it yourself at home. $19.49 for 9 gallons of gatorade is way better than paying retail price for a quart at a time.

As I understand carb loading, it's not something you can do for a repeated effort like a daily commute. The idea is to deprive your body of carbohydrates for a period of time, then binge shortly before an endurance effort. You can't really achieve a level that would be useful inside a repeating 24-hour period.

Lastly, don't sweat protein. It probably wouldn't hurt, but any benefit would be extremely minor for the workloads you're doing, and isn't worth significant effort or attention. Again, just keep up with the cycling and your body will quickly begin to adapt automatically.

Edit: Oh, and one thing that will help is to consume carbohydrates immediately after your commute. The human body absorbs carbs significantly more quickly after a workout, and uses them to replenish any lost stores. Waiting even a half hour greatly diminishes this effect, so the sooner the better. It doesn't have to be a full meal or anything; anything is better than nothing.