Are there particular foods or medications I should avoid while I'm taking alavert?

Yes. Some relatively unusual medicines for heart rhythm problems (amiodarone), some medicines for diabetes (pramlintide or symlin) should not be used with alavert unless you have discussed it with your doctor. Also talk to your doctor before using other antihistamines (like claritin, (loratadine) benedryl, atarax, zyrtec or the like) or drinking alcohol. Foods are not really a problem.
Antihistamines. Avoid any and all alcoholic beverages as well as taking additional sedating medications not prescribed by your physician. If you are unsure of a possible interaction, don't be foolish, call and ask your doctor before experimenting.