It will depends on the downstream use of the sample. For RNA, DNA, proteomics analises?

I would not use any buffer at all. As long as you keep the specimen sealed (in a tube or in plastic).

It depends on downstream application as rightly told by Bustamante-Filho. If you are focusing on RNA, tissue samples should be stored in RNAlater RNA stabilization Reagent (e.g. Qiagen); For DNA and proteomics studies it should be washed in PBS pH 7.4, the solution is then decanted and tissues are stored at -80°C in a sealed tube/vial.