Enough for a day or two of basics is the right target: airport transport to your accommodation, a couple of meals, tips where customary, a SIM card, and a small buffer for surprises like a deposit or a cash-only shop. Think in terms of what those things cost at your destination rather than a fixed sum, since a day of incidentals in one country buys a week in another.
A sensible pattern is to carry that starter amount in local cash, obtained before departure or from a bank ATM on arrival, plus a backup stash of a widely accepted major currency for emergencies. Keep it split between two places, some in your wallet and some in your bag, so a lost wallet doesn't strand you.
Ask for some small denominations too; taxis and street vendors often can't break large notes, and that's a genuinely common first-day frustration. Once you've confirmed your cards work locally, you can stop carrying much cash at all in card-friendly countries.