Short answer
Bring enough cash: card payments are rare outside Ha Giang town and ATMs are limited in the highland towns. Buy a local SIM or eSIM before you set off — mobile coverage is good in towns but patchy in the deep valleys.
Cash
Most homestays, small restaurants and shops in the highlands only take cash (or Vietnamese bank transfer). Withdraw enough in Ha Giang town before you leave. Around Tet (in 2027, the holiday runs from 4 to 10 February) many shops and services close for several days, so carry extra. For a full budget, see how much a Ha Giang trip costs.
ATMs
There are ATMs in Ha Giang town and in some highland towns, but they can run out of cash at busy times. Don’t rely on them.
SIM and eSIM
A local SIM or eSIM with data is useful for maps and for contacting your accommodation. Buy it in Ha Noi or Ha Giang town.
Coverage
Expect good signal in towns and patchy or no signal in some valleys and on parts of the passes. Download offline maps before you go.