I always travel with an e-ticket which is simply a print out from my email. The only thing on it that is important is the confirmation code or number. I have never been asked for this upon entering Thailand. I would make sure the departure card is filled in with a flight number though, the blank boxes will probably draw attention.

On a side note, it depends on your actions and appearance whenever you do anything that involves a security check. Not to offend anyone or be judgemental, but I have seen slovenly backpackers with foreign debris stuck in their nappy dread locks stopped at every security checkpoint with their belongings dumped and scrutinized. I think the average, clean, non-offensive human being that has their documents in order and doesn't blatantly leave off information that officials need to see will get admitted without any problems. Before I leave for any airport, I always shave, shower and put on clean clothes that cover up my tattoos.