LOL I found the whole idea of someone worrying what to wear in Bulgaria amusing, really.  But up to the point:
1. No athletic shoes – especially white...mmmm why not? You can wear white, especially in summer
2. No t-shirts with writing ...then again - why not? Many people here DO wear those kind of shirts even with signs in English. As long as the writing isn't very rude I see no reason to bother. Just keep in mind these are popular withing younger people, but if that doesn't bother you - nobody here will be impressed either way.
3.Not so much on wearing jeans? ...everybody wears jeans here
4. Don’t wear shorts... Summer in Bulgaria is usually hot and many people - both men and women wear shorts of all kinds - long and short, dark and white...
5. Don’t carry camera bags ...You can carry whatever camera bags you want. Being tall and blond means people will acknowledge the fact you are not Bulgarian anyway, so just take whatever is comfortable for you, none will be impressed or notice that anyway.

In summary: you cannot blend with people or go as a local but that should not bother you much. People here don't pay attention on your clothing and bags, we are used to see many tourists in summer from various countries, especially if you plan to visit the Black Sea cost - there is the total mixture of clothes, styles ect...

Most important - enjoy your stay here and bring your good mood and smile, Then you will be just fine :))))