Infinite Jump:

Spam jump under a low ceiling, click the "I'm Stuck" button, or move into an area with an open ceiling. This will cause you to jump into the air. The height of your jump depends on how many times you click the space bar while under the structure.

Entity surfing:

Stand on top of an entity (Trash Can, Trash Bag, Box, Wheelchair, Basketball, etc), then jump and pick up the item in rapid succession, causing you to jump into the air.

Carhood Glitch:

Stand, then crouch on a moving car to launch it into the air.

NPC Relocation:

Kill a vendor NPC. The NPC will respawn and stay wherever you move their body.

Basketball flying:

Pick up basketball, look all the way down until the basketball starts to glitch, then hold the walk backwards key.

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Let me know about any other glitches you find, and I'll add to this forum and make a video displaying it.

Not sure if you would consider it a glitch but when spamming jump while riding the golden skateboard, near infinite acceleration and speeds can be achieved.

Also shelve storage in this game is notably buggy, Using the configured setup below can be used to clip out of bounds, although has limited practical usage. Though it is possible to actually clip inside of the shelves themselves, allowing you to ignore collision and pass through walls until you no longer remain out of bounds, it is much more difficult to perform in a controlled environment unless a better shelving glitch setup can be achieved.

Walk forward into the shelves, hold left. This also works when a very large amount of shelves are placed side by side. More shelves = More buggy

Another mechanic that I'd like to further add is police will refuse to shoot you if you are close enough in range to be arrested regardless of your current heat status. Holding the walk backwards key while using a melee or ranged weapon against police officers becomes extremely efficient. Where certain situations in a speed run may call for a player to take more evasive actions to avoid police, this method allows them to be directly dealt with while still maintaining travel distance towards your intended destinations.

If I find anything else I'll be sure to contribute more to this post.