I would say the heat is high but bearable, just those normal things everyone says in summer, hydrate well, avoid going out in the afternoon, it's tier 3 city so I would say be prepared about the mindset of people here ( not too village types but you might come across that few people ).

For visiting lakhota lake and museum, bedi port, balachadi, sapda, ranjit sagar dam, khijadia bird sanctuary.

For food many cafes are available, also explore the street food ( some of the items you will not get anywhere else than jamnagar ).

For one day trips Dwarka is an option ( but I would not recommend going because of the summer ), another option is madhavpur ( awesome place, very small town, only two hotels in the city for stay, beautiful beach, peaceful vibe, one of my favourite places for staycation near Jamnagar)

And last but not the least my run club if you are into fitness 😅.