It's a good idea to have some cash on hand. Especially when you're exploring bustling bazaars, hopping onto public transportation, or indulging in street food, cash is king. Smaller establishments, local markets, or traditional teahouses might not have card facilities. Plus, when it comes to haggling in places like the Grand Bazaar, cash can sometimes get you a better deal. So, while you don't need to carry a hefty wad of bills, having a mix of both card and cash is the smart way to navigate the vibrant streets of Istanbul.