If my period's late, does it last longer?

So, I am 15 and I just got my period, 100 days late, and it actually fit pretty well as I am going to Greece in about a week and a half. But I am in doubt about something: if my period's late, does it last longer? I normally have my period in 6-7 days, and I need to know if I have to bring tampons and stuff.