Prefer Liquid nitrogen if you have, second choice will be -80C

Alternatively, you can make small pieces of tissue in RNA-Later and store in RNA-Later and follow temperature instruction written on bottle that allows you store at room T or 4C or other options

If you can get RNA later, they were good in preserving RNA, if you want both RNA and Protein snapfreeze will be a better alternative as Subhash recommend and aliquot portion for RNA and protein. The ower the temp. the longer the shelf life if you have access to -80c freezer we can retrieve mire than 5 year old sample with good RNA yield compare to -20C.

Thank you