(at around 1h 6 mins) While Eddie is holed up at Coit Tower trying to find Cletus, several helicopters pass by looking for Venom and Carnage. This was actually not planned; the helicopters flying by were actually part of the shoot for Matrix Resurrections (2021), which was filming in the same part of San Francisco as Let There Be Carnage during their shoots. Instead of waiting for a clearer shot, Andy Serkis thought it would make sense for helicopters to be roving around during the scene and left it, adding additional dialogue by Tom Hardy in ADR afterward to mention them.
When Eddie and Venom are arguing with each other in his apartment, Tom Hardy recorded lines as Venom which were played back (in an earpiece Hardy wore) by a sound operator. This technique let Hardy improvise his dialogue as an exasperated Eddie.
(at around 15 mins) When Brock enters Mrs. Chen's shop, Venom arranges a stack of magazines for her. On the cover of those magazines is Marvel writer Stan Lee.
Venom discards all red M&M's before Carnage is seen by Eddy or himself. This is because Venom is scared of "the red ones". He uses this term when referring to red Aliens such as Carnage. His fear leads him to retreat when seeing Carnage for the first time.
(at around 15 mins) Venom greets Mrs. Chen with "Wan shang hao!" or "Good evening" in Mandarin.