Firstly the game is impossible without object highlighting. I have only found 2 weapons and practically nothing else.

I have got to the place where you use the token to get the train/tram/cart ticket (just after you used the lift in the Devil's Pit Stop).
And then you slide past the dumpster to get to the gate but I can't open the gate.

Anyone know how ?

You have to search the nearby buildings for a set of clothes to change into. They will contain the key that unlocks the gate.

Unless I'm thinking of a different gate. Is there a generator in the area you slipped into? If so, turn that 'sucker on.

To get your tram ticket:

Thanks so much I would of been looking for ages I had passed those clothes so many times and had never even thought of interacting with them.