What disease prevention does my dog need for travel to Bosnia/Croatia?

Advantix is not protecting you dog against heartworm so it's not a very good option, you would want a product that covers also for heartworm such as Revolution or Advocate (although heartworm is not a real concern if you live in Bosnia). here is alink that will provide you all the information you need regarding heartworm: https://www.heartwormsociety.org/pet-owner-resources/heartworm-basics

According to the article I will link below, vectors that carry heartworm (mosquitos) have been found in Bosnia and Herzegovina, so I would speak to your vet to see if they have seen cases of heartworm in your country. If so, I recommend giving Bella Heartgard. It's an excellent heartworm prevention. She has to be tested for heartworms first before it's safe to give her the medication. Bad breath is a sign of a dental problem in dogs, and while you can brush her teeth at home, I would have Bella seen by a vet. The bad breath can be caused by severe gingivitis, tooth root abscess, or a broken tooth, all of which can only be treated by a vet. If you do want to start daily brushing of Bella's teeth, make sure to use a dog toothbrush and a dog toothpaste. Human toothpaste contains ingredients that are toxic to dogs, and can never be used on Bella. You can get her a toothbrush and paste from a pet store or online. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3372948/

Most treatments are available throughout Europe for canine babesia but as the condition is rare in the U it may not be in stock at the clinic. I recommend you email your vets office with (a) the particular parasite that has been diagnosed and (b) the current treatment she is receiving so that they can source it and have it in stock. Products which are ordered in to treat rare cases can be very expensive

Double check with your vet that all the requirements for transporting Bella across the countries are met. I wouldn't introduce any new snacks since it could cause upset stomach. Simply observe her normal feeding times and stop for a quick walk and potty break every few hours. Make sure to keep her on a leash and be watchful of your surroundings when stopping.

Have her tested for heartworm before you travel and start her on a preventative if her test comes back negative. It should be given monthly if you will be overseas for an extended period of time. Options include HeartGard, Revolution, Trifexis and Advocate topical.

I would recommend looking into the requirements for your dog to travel to this island. Most islands are rabies free and you will need a rabies titer which can take 6 plus weeks to get back. this titer has to be sent to a very specific lab and also you will need a international health certificate writen by a usda vet. It might not be worth the stress and expense of travel to take him with you for a vacation

There are no proven safe or effective home remedies to prevent fleas and ticks in dogs. Since ticks (and even fleas) can carry some nasty disease, Pudgy definitely needs protection! I love Seresto collars for their protection. Advantix or Frontline Plus are topicals that you can get over the counter, but in my opinion they do not prevent fleas as well as Seresto collars or prescription oral preventatives. Even with protection, you should still check Pudgy every night for attached ticks - don't forget folds around the ears or toes! Pudgy will probably be okay for the trip without being current on vaccines, but I think he should have them updated as soon as you get back if he wasn't done with his recommended series. Just make sure he isn't around other unvaccinated dogs.