Yes, vegetarian options are available on most Culebra boat excursions — lunch is typically included and can be made vegetarian with advance notice.
On standard full-day tours (Flamenco Beach, Culebrita, Luis Peña snorkeling), the usual lunch is a beach picnic or barbecue: grilled chicken/fish, rice, beans, salad, fruit, bread, and soft drinks. Vegetarian adaptations are common and easy — operators replace meat with extra vegetables, beans, rice, plantains, cheese, or eggs (if lacto-ovo). Many tours already have veggie-heavy sides (rice & beans, salad, fruit) that suit vegetarians even without special request.
Vegan is more limited (due to rice cooked with oil/butter or cheese in some dishes) but possible if you notify when booking — guides can arrange fruit, rice, beans, salad, and plant-based snacks. Always mention dietary needs in the booking notes or call/email the operator 24–48 hours ahead — reputable companies accommodate vegetarian/vegan requests reliably.
You can bring your own snacks (energy bars, nuts, fruit) if you’re very strict — most boats allow it.
You can book highly rated Culebra boat excursions (Flamenco Beach, Culebrita snorkeling, with vegetarian/vegan lunch options on request, snorkel gear, and guide) at Culebra Tours.