When I need chicken breast I do the following: First, Iif I am shirt-less, I put on a shirt.

Or just "I put one on".

I take my bike, open the door, and being at the threshold I make sure that I have the keys of my bike's lock keys and my mask (here for, to entering to a supermarket it is necessary to usewear a mask).

"entering to a supermarket" is a grammatical error - the rest of this was grammatically fine, but complicated or unusual usage.

I stop some meters before the entrance, at a place where a big and long guardrail lies, and lock my bike to the rail or to one of its posts.

Or just "where there's a big long guardrail".

I enter to the supermarket, and go directly to the butcher shop.

Or just "the butcher."

If there is someone waiting, I just stand in line after him; if not, I ask the butcher for one big chicken breast or more (depending on the day and the money I've got).

This butcher shop has its own employees and is in some sense independent from the supermarket, but you should pay for your order inat the supermarket's cash registers.

"You should" is okay, but it gives the sense that you're giving us personal instructions, like we might go to the shop and need to know what we should do to pay. I *think* you just wanted to use "you" as a generic you, and I wouldn't say "should" in that case.

"the cash register" - here means there's only one. As there's multiple, "a cash register" or "the cash registers".

I go to the registers and select the one with less people or less things to be payin the queue (because sometimes there is only aone person with a big load of shopping).

I go out and do the formearlier actions in reverse: unlock the bike, get on the bike, ride it to my samhouse, make sure I have the chicken and the change, and finally I throw open my door and take off my shirt.

I think you mean the place you live, but I can't guess why you said "my same".