Well, if you take out the helicopters(I usually just try avoiding them) then they can't set off a siren calling all the special ops over. Shotguns are good to take out the special ops, I usually use a hunter's knife/cleaver and they die within 4-5 slashes. The lead pipe is good too.
One way to get to the supermarket without having to go through too many army guys is in the hallway towards the gunstore. If you face the opposite of the gunstore in the hallway, you'll see an empty room with a back door to a back hallway. There'll be dead zombies(I think security zombies); Anyway, go all the way down the back hall and there's a doorway on the left, but be careful because there's 2 special ops through the door. move the camera around so you can see inside the room so youcan time your attacks on them. after you kill them, there might be 2 more army guys coming after you, it varied when I did it. Kill them then make your way to the grocery store, but there's a lot of special ops in there just so you know. Then make yourself towards the Pharmacy where you got the medicine. Then after this you can do 2 things; A) If you got the Maintenence Key from down in the garages, you can go down to the garages and get into the van and drive to the next location or B) You leave the grocery store and get on Isabella's bike, which is in front of the grocery store, and go to the next location.