A few years ago when I was still flying I started adding Linseeds to appropriate meals as a supplement (Omega 3's and all that). I noticed on subsequent flights I was developing more "trapped gas" and sometimes not so trapped... I cut out the seeds and the problem reduced enormously. Also fizzy drinks are a cause too and try not to gulp your food down because you'll end up swallowing a lot of air with it, chew thoroughly before swallowing.