@WanderGuy,
First of all, welcome to a2k, WanderGuy... from a well known a2k nut about Italy, which I didn't get to until I was almost fifty. Travelled in Mexico in my twenties, though.
I, like many others, would enjoy knowing where you are thinking of going.
Second - please come back to a2k and tell us about your trip, when you get back, or even on the trip if you feel like it.
Third -
advice, if any, from me.
Well, I used to eat best for lunch and just go into an alimentaria (corner store type place - except way better than, say, 7-11s) for bread and cheese or salami or roman artichokes, maybe an orange, and one piece of candy, for dinner. I found wine pretty inexpensive in italy, compared to the US, but that was a while ago.
I didn't stay at hostels, being an older cranky female, but now that some hostels have mixed ages I might if I were going there again. What I did do was hit the tourist info office in town upon arrival - and look at their One Star accommodations.. They would have lists of pensiones and alberghi, and I liked virtually all of the places I grabbed from their lists.
Well, that was on one trip. Another I made reservations beforehand, but that was a much tighter schedule.
Fourth - take really really comfortable shoes, because walking and looking is a lot of the fun.
Fifth - go light. I'd take the let's go guide or lonely planet, but torn up so it wasn't heavy, just the pages you could really use.
6th - the time I just took a duffle for 29 days, I bought a travel smith suit with a second pair of pants, and a few tee shirts/blouses - and that was about all.
I wanted to burn the suit when I got home, but it had been washable (showers - consider bringing a couple of hangers) and I'd had almost as much sentiment about it as desire to burn and bury it. Being older (etc), a black suit worked for me. Could be anything, but figure you'll learn to hate your clothes.