I, too, have heard from reliable sources that most of the stuff you hear on this subject is wives' tales. Of course, there are exceptions, like alcohol and some medications.
The only way to know for sure is to try giving something up - one thing at a time, really - for 3 days, then reintroducing it. I found that my babies were pretty sensitive to caffeine, much to my chagrin. I gave up all caffeine for the first few months of breastfeeding.
Things that I found helped:
1. In the first few weeks, and for the following several decades at least, the more sleep the better. Read Mark Weissbluth's 'Healthy Sleep Habits, Happy Child' if you can find the time - most useful book I read EVER.
2. You've probably heard that you have 'foremilk' and 'hindmilk' - what your baby gets when you first start breastfeeding versus what comes a bit later. It seems that foremilk generates gas and hindmilk neutralizes it. Gas is a natural thing, helps everything move along nicely. If you feed longer on each side (your breasts are never actually empty), you may find that the gas gets MUCH better. I so wish I'd known this with my first baby - it worked a treat with my second. You might try feeding off one side only, but let her go on for as long as she cares to.
Hope this helps. If not, be comforted by the idea that by 3 months of age, her digestive bits will be much more mature, and the problem should resolve itself. And in the meantime, carrying her like a football (putting pressure on her tummy with your arm) can help, as can bicycling her legs.