Food taboos and behavioral taboos both exist nearly everywhere, and the food ones are usually the most codified. Pork is prohibited for Muslims and Jews, beef is deeply taboo for most Hindus, and many Buddhists and Jains avoid meat entirely, with Jains also avoiding root vegetables. Alcohol is forbidden in Islam and restricted or banned in some countries, so never pressure anyone to drink or assume alcohol is a safe gift.
On the behavior side, common sensitivities include eating with the left hand in South Asia, the Middle East and parts of Africa, sticking chopsticks upright in rice in East Asia, and refusing offered food or drink too bluntly in hospitality-driven cultures, where a soft decline works better than a flat no.
Conversationally, avoid joking about religion, mocking dietary rules, or asking pointed questions about why someone does or does not eat something. Politics, personal income and family matters can also be off-limits until you know people well, though in some cultures those same topics are fair game. Follow the locals' lead and let them open the sensitive doors first.