Best Buy offers The Secret Life of Pets on Blu-ray / DVD / Digital HD bundled with a Sing Lunchbox for $12.99. Opt for in-store pickup to dodge the $3.99 shipping fee. That's at least $4 less than you'd pay for just the movie at another local retail store.
Carry your lunch in a paper bag? Amazon offers the movie alone for the same price with free shipping for Prime members.