It's no problem carrying the GPSr in your carry-on baggage.
It may be a problem if you try to use it during the flight, though. Many airlines prohibit their use. However, I recently flew cross country on Northwest and asked the captain while boarding if it was OK to use, he said "sure". It was fun to see speed, altitude, and our position on the map.
Have fun in Vegas...there are about a half dozen virtual caches on the strip. I did several when I was there a couple weeks ago.