Welcome to the habit.

Now, RELAX!

Go on your holiday with the one lens you already have, and enjoy things. But as you shoot away in the USA, note where you'd really liked to have done something different -- faster exposure, different perspective, etc.. -- and keep that in mind for later.

Once you're back from the trip, write a little script to snarf the EXIF data from your photos, and look to see how often you used various focal lengths from the lens you have.

If a significant number of photos were at the limits of the lens (long or short end), then this tells you that you might appreciate a wider or longer lens to extend the range. Your own shooting habits will determine this.

If most photos were between the extremes, then you could consider getting a higher quality lens to cover the midrange, perhaps one with a wider aperature to allow more artsy shots and/or faster shutter speeds (less blur).

If your shoulder/neck are sore for weeks after the trip, then perhaps instead you should just sell it all and get a better compact all-in-one to avoid that on the next trip!

Cheers