so far I have found 3
1: on the right end of the map near the 2 houses, if you noclip over the barriers you will see a wall with a cheaple wearing a black shirt. if you approach it the stalker scream will play and you will be flung away from it.
2: if you noclip PAST the wall, you will see a house that is actually visible from the gated off path not too far away. what you CAN'T see from the gate is on the right side of the house. if you go there, you will see one of Squidwards paintings from Spongebob.
3: there is another gated off path near the left of the map. if you go to it, you can see a shed with a garage. if you noclip into the shed, it will have purple lighting, and you can see two skulls and a cactus pot. (don't ask me what this means because I have no idea.)

if anyone else finds any other easter eggs, post them in this discussion!

(UPDATE)
if you go to the red cabin on the hill and break all the crates, you will see this
https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=3412548111
here's what I can make out from the text: (there are probably some mistakes)
intro 1:11
hot dog 3:50
my generation (i couldn't make out the number)
sushi occasion(?) 4:57
my way 4:33
rollin' (air raid vehicle) 3:34
livin' it up 4:24
the one 1:42
gecha goodbye on 4:29
take a look around 5:18
(i couldn't make out the worlds) 5:66
boiler 3:47
hold on (couldn't make out the number)
rollin' (urban assault vehicle) 8:33
outro 2.61

none of that made sense LOL