During the episode entitled "9:02", an electromagnetic pulse hits the town of Jericho. As a result of this, all computers cease to function, including those found in newer automobiles (~90-present). Despite this fact, many of the following episodes have shown recently manufactured vehicles in proper running condition.
When Gracie first notices the missing pesticides (camera angle toward the front of her store), one of the gray buckets of pesticides is very clearly visible in the bottom right corner of the screen. The camera angle then changes showing a bunch of Fram oil filters and nothing but empty shelves beyond that.
When Hawkins is teaching his daughter to shoot, she is wearing ear protection, but he is not. As he's instructing her, he's speaking too softly for her to hear him clearly with the type of earplugs she's wearing. Furthermore, as close as he's standing to her as she's firing, after a few shots, his ears would be ringing, causing him to speak much louder than he does.
Antibiotics has no effect on a flu, which is caused by viruses not bacteria.