Traveling with marijuana is legal. Kind of. Sort of. Barely. Because marijuana is still illegal at the federal level and only legal at the state level, traveling with weed is kind of a legal mess. The good news is that so long as you are staying within Washington's confines, you are pretty much good. Travel across state lines and things become more complicated, even to Oregon where marijuana is also fully legal.
Let's break it down.
The short answer (and the easiest) is no.
Unless you have a medical license, you can't board an airplane with marijuana. (Or, at least you aren't supposed to.)
This includes trips to other states where marijuana is legal, such as Oregon and California, and even between Washington cities, such as Seattle to Spokane.
However, marijuana isn't the Transportation Security Agency's highest priority. If TSA agents discover marijuana in your luggage during the preflight screening in Washington, they simply hand it over to the local police department. In Spokane, you might just be asked to simply toss it.
As long as you aren't high, it's perfectly legal to drive with marijuana in your car so long as it is either 1) in the trunk of the vehicle; 2) out of reach of the driving area of the vehicle; 3) or in an unopened container, according to state law.
Just be careful at the border.
Transporting marijuana from Washington to Idaho is illegal. Taking marijuana from Washington to Oregon is also technically illegal, despite the fact that the state has legalized recreational marijuana.
Traveling to Canada?
Also a big no.
Our neighbors to the north fully legalized marijuana in 2018 across the entire country. However, traveling to and from Canada with any amount of pot remains illegal, according to the Canada Border Services Agency and the U.S. Border Patrol.