Do you need a reservation to just order a drink (and maybe an appetizer)?

No, you can order at the bar

If you go right at 5p about 25% of tables are left open for walkins. There is also first come first serve at the bar.

reservations are better .otherwise long wait time.

No reservation required to eat at the bar, though even that can get crowded during peak times

No. You can drink + eat at the bar