Adolescents and young adults with food allergies are at increased risk of adverse events, including death from anaphylaxis. Epinephrine is the cornerstone of emergency response, yet few individuals with serious food allergies consistently carry their emergency medication. Behavioral economics offers promising, previously untapped opportunities for behavior change in this arena. To test the effectiveness of modest financial incentives in promoting the carrying of epinephrine and to evaluate the acceptability of text messaging for delivering reminders and key health messages to young adults with food allergies. A mixed-methods randomized controlled trial in young adults with food allergies investigated the carrying of epinephrine auto-injectors using financial incentives plus text message reminders vs text message reminders alone. Epinephrine carriage was assessed 10 times during the 49-day intervention using rapid-reply cell phone photographs plus daily code words. The intervention (financial incentive) group had their epinephrine auto-injectors at 54% of check-ins vs 27% of check-ins in the control (text-only) group (P = .023). Participants in the 2 groups consistently reported favorable impressions of text messaging as a desirable, unobtrusive way to receive information and support for food allergy management. Although the intervention and control groups reported favorable impressions of text message-based reminder systems, the intervention group performed significantly better than the control group on a photograph-based measurement of epinephrine carriage. There remained ample room for improvement in the 2 groups given the goal of consistent, uninterrupted epinephrine carriage by people with potentially life-threatening food allergies. https://clinicaltrials.gov; NCT02354729.