Most of the interior scenes were clearly shot inside businesses that were closed for the night, and this is most apparent when Rod and Nathalie go out to a bar & grill after Rod meets Nathalie's mom. The only other people we see in the restaurant are the waiter and the singer!
Same with exterior shots near roads, where they couldn't get any temporarily halt on traffic driving by. Yes, your apocalypse is quite believable seeing a steady flow of traffic driving the speed limit behind your characters.
One example of Improvised Weapon. According to Whitney Moore, James Nguyen elected to have the actors use coat hangers as weapons rather than a shower curtain rod as scripted. Why? Because the Motel 6 they were filming at didn't have rods in their showers and apparently it would have broken the film's budget to go to a hardware store and spend $8-$16 to buy one.
The film has no music budget either, because most of the music is taken right from a catalogue of royalty-free production music and reused blatantly, give or take a few original compositions (and Hangin' Out). RiffTrax notices this right away:
Bill:(as Nguyen) Hi, I'm making a film and I'd like to pay you for a full score... wow, that much, huh? Well, how about a one minute song and we pause it and loop it again? Deal!
Mike:(as Nguyen) Hi, I'm making a film and I'd like to have it open on one of those long driving shots, you know, where you follow the car from above through a nice landscape... ooh, wow, that much, huh? How about if I just shoot from inside the car with a crappy home video camera? Deal!
During the "news" segments, viewers will notice that Nguyen couldn't even afford to have the Getty Images watermark removed from the stock footage.
They had to do one scene in a single take, because they didn't have the money to buy anymore cartons of orange juice, the prop that stood in for the bird's acidic saliva.
Inverted when Rod is talking to Natalie over the phone after her photoshoot. He actually has an iPhone while all the other phones in the film are flips. Though it's entirely possible that was the actor's personal phone.