Hi, if such Karyana store is engaged in prepacking of items before selling to customers, then yes it is required to make declarations under the provisions of legal metrological act, 2009. However if it is selling loose items or prepacked items that are packed by manufacturer or wholesaler and not itself, then he is exempted from making any declarations.
For second question, yes gst is applicable on sale of such items. As per FAQs released by CBIC, In the context of food items (such as pulses, cereals like rice, wheat, flour etc), the supply of specified pre-packaged food articles would fall within the purview of the definition of 'pre-packaged commodity' under the Legal Metrology Act, 2009, and the rules made thereunder, if such pre-packaged and labelled packages contained a quantity upto 25 kilogram [or 25 litre] in terms of rule 3(a) of Legal Metrology (Packaged Commodities) Rules, 2011, subject to other exclusions provided in the Act and the Rules made thereunder.
Meaning, if dal, chawal, gram etc is prepacked in packages upto 25kg or 25 litre, then it will attract gst @ 5%. However, if package is more than 25 litre or 25kg, then it is exempted from GST.
Hope the above shall suffice.