Trying to plan ahead so any know if card payments are common at hostels in Eritrea or cash is king?
I'd be very cautious about relying on a card for payment. Hostels are not equipped to take cards, and even ATMs are not available for foreign cards. The best plan is to bring US dollars or Euros and exchange them for your hostel payments and other daily
Forget cards entirely. The financial system in Eritrea is a cash-based one. There are very few places that even have a card reader. For any hostel or guesthouse, you will need cash in Eritrean Nakfa to pay for your stay. Plan accordingly and bring money to exchange. The black market exchange rate is much better than the official one, but it comes with risks.
You'll be using cash for everything. I was in Asmara last year and did not see a single place, not even a hotel, that accepted a credit card. The hostel you stay at will be cash-only. I'd highly recommend bringing US dollars or Euros in a safe place and exchanging them at a bank when you arrive. Do not rely on finding a working ATM with your foreign card.
Cash is absolutely king, and you'll need to bring it with you. Eritrea has a very underdeveloped financial system, and credit card acceptance is virtually non-existent, even at major hotels. You will not find any hostels that accept cards. The local currency is the Eritrean Nakfa. Your best bet is to bring US dollars or Euros with you and exchange them, as ATMs are not available for foreign cards.