All passengers are entitled to bring 1 small personal bag on board which must fit under the seat in front of you (35cm x 20cm x 20cm). Examples include, handbag, laptop bag and small back pack. https://www.ryanair.com/gb/en/useful-info/help-centre/faq-overview/Baggage#0-1
https://www.ryanair.com/gb/en/useful-info/help-centre/faq-overview/Baggage#0-1