As a 54-y.o. old fart, I'd say the most important thing is not to get roped into paying 18% interest on a credit card balance. Regardless of anything else, that will eat you alive.

Money means little to me now. I could take 10 trips to Europe financially, but I cannot get away. Time and availability is everything.

Looking back 35 years and talking to my 19 y.o. self, I'd say "What you have now is time. Burn it. You don't have a job, or a spouse, or responsibilities, or monthly payments, or ailing parents to hold you back. DO STUFF."

Travel cheap. You can do it while your body is limber and you can sleep on overnight trains and ferries without pain and you can get drunk and be up at 6 am with vigor and you can live on bread and cheese and salami and beer and wine. Sleep in train stations, or on the beach on a Greek island. You are free.

You have fewer boundaries than I. Take advantage.