Not the usual "pack sunscreen" advice. Five things that actually matter once you're on the ground in Sri Lanka.
Don't overplan the food. Sri Lanka has fantastic rice and curry, kottu roti, hoppers, and fresh seafood — but eating well doesn't mean you need a reservation book. The best meals I've had were at roadside places with plastic chairs and a glass counter. If the place is full of locals at 1pm, walk in. If the menu has photos of everything and an English name that sounds like a chain, keep walking.
The train bookings game changed. The scenic Kandy–Ella train used to be a scramble, but you can now book reserved observation car seats online through the Sri Lanka Railways site. Do this at least two weeks ahead during peak season. The unreserved carriages are chaos — fun for 20 minutes, exhausting for 7 hours. Book ahead or don't bother with the long haul.
Your driver is not your tour guide. Private drivers are phenomenal for getting you from A to B, and many have solid English and good restaurant recommendations. But they're drivers, not licensed guides. If you want deep history at Sigiriya or Anuradhapura, hire a separate site guide. They cost $10–20 and they'll spot details you'd walk right past. Your driver will happily wait while you tour.
ATMs dispense large notes — break them early. The machines spit out 5,000 rupee notes (about $16), and street vendors, tuk-tuks, and small shops can't break them. Buy something small at a supermarket or a slightly nicer restaurant to get change. Hoarding small bills is a survival skill in rural Sri Lanka.
The dress code for temples is real and enforced. Cover shoulders and knees. Take your shoes off. Women don't need to cover their heads at most temples, but men should remove hats. The Temple of the Tooth in Kandy is strict — no shorts, no sleeveless, no shoes inside the inner sanctum. They'll turn you away at the gate. Bring a sarong in your day bag, it works for everything.