I have flown Internationally many times. What I do is... have knitting already started on bamboo circs.. and I just don't say a WORD about the knitting as I go through the security check point. They know that I have knitting w/ me.. no need for me to point it out to them to draw attention to myself or my knitting. I'm not hiding anything- I already know that I can carry my knitting w/ me.
I've had no problems. I usually just keep my knitting in a big zip log bag/etc. NO scissors.. I just put a 'dental floss' container in there.. you can gnaw the yarn across the blade to cut it .. if you need to do so.
Some countries.. might not want you to be knitting from their country to the STATES.. *You can find that out on the sites or ask 'after you arrive' to your foreign country. IF they say 'no'.. then, simply put them in your checked bag for your return flight.
If it helps any: I have flown both to/from Korea to the states w/ no problem.
I've also flown to/from Italy (as late as less than 3 years ago) to the states w/ no problems. These are the countries in the past 3 years- I've flown to many more countries than that.. but, rules have changed a lot lately.