You actually CAN drink moderately during lactation, it just depends on timing. For example, if you have a single glass of wine or a single beer immediately after you've last nursed/pumped, it takes 2-3 hours for your body to completely metabolize the alcohol. It doesn't get "stored" in your breasts, so if baby goes to bed at 7pm, you have a glass of wine with dinner, then baby wakes up at 1am to eat again, you're fine. No alcohol gets to baby.
As far as things like caffeine, dairy, gas-inducing foods like cruciferous veggies and etc... it's different for every baby. My son was never bothered by me consuming caffeine or by anything in my diet, but some babies are very sensitive and mom may find she has to eliminate certain foods while nursing. There's no need to cut anything out (except for meds known to not be safe while breastfeeding) from the get-go. Have your baby, establish breastfeeding, then if baby seems to be having trouble with sleep, gas, reflux, etc, *then* you can experiment with an elimination diet and see if that helps.