Where are you starting and ending up? Neither Veliko Tarnovo nor southern Serbia is particularly close to the places you mentioned in Romania.
Romania has some handsome cities that Ceausescu didn't get around to rebuilding in concrete. Brasov is one of them.
That part of the Balkan peninsula is rather poor, so you might benefit from doing some research on restaurants ahead of time. It wouldn't surprise me if a lot of the best restaurants are in high-end hotels. I remember a comment somewhere along the way (perhaps from Rick) back before my 2015 trip that Romanians couldn't really afford to eat out. My impression was that Bulgaria was no wealthier and ingredient quality could be an issue. I ate a lot of chicken kebabs. Veliko Tarnovo gets a lot of tourists (there was an Asian tour group at my hotel), so it has a lot of restaurants. In other places there weren't so many.
On Serbian menus you're likely to see several sauces/dips listed as add-ons. They cost only about the equivalent of $1 US at the time of my trip and were very tasty. Definitely try those. Serbia also has a flaky pastry (I think originally Turkish) sold at stands and probably also in bakeries. I don't remember whether they call it "borek" or something else; that might be the Turkish name. I had it, at different times, stuffed with salty cheese or sweet cheese. It's quite oily, so those with sensitive stomachs should be careful about consuming too much, and if you buy it to consume later you would do best to have a plastic bag with you.
In Romania I enjoyed the fresh-baked, ring-shaped bread (like really stretched out bagels) called "simit"--though I think you might run into them under another name. I suspect they, too, came originally from Turkey or the Middle East. You can get simit plain or with seeds on the outside. Once I found them with coconut, and I think they might sometimes be prepared with sweetened cheese or perhaps chocolate inside. They're a nice breakfast or snack to munch on while you walk around. I saw them being sold from street-side windows in bakeries all over Romania.