What should I bring on my first scuba dive?
For your first scuba dive, bring what keeps you comfortable, protected, and ready to focus on the experience. A swimsuit or rash guard is fine under your wetsuit. You may want sunscreen, but I personally prefer wearing a long-sleeve sun shirt instead of covering myself with lotion that will wash off in the water. A towel, water bottle, and small dry bag for your phone, keys, and wallet are also useful.
If you have personal gear such as a mask, fins, snorkel, and boots, bring them even if the dive shop provides rentals. Familiar gear always fits and performs better. One item I strongly recommend bringing is your own mask defog. Every diver has their preferred brand or formula, and I find the boat versions or communal bottles less effective. A foggy mask can ruin a dive faster than almost anything else.
Beyond gear, bring patience, curiosity, and time to listen during the briefing. The less you rush, the more enjoyable your first dives will be.