DIY treat - freeze your guinea pig's or bunny's favorite fruit or veggie treat into ice cubes and give them as treats. This helps them cool down on summer days. Remember to always check with your vet before introducing human food to your pets.
Keep your bunny cool in hot temps. Rabbits get heat stroke easily, this gives tons of great ideas on how to prevent that. - I used the frozen soda bottles when raising rabbits in California they worked great!