Est-ce
Est-ce opens the yes-or-no question about whether everything is available before leaving. It works at the beginning of the question structure used here, before the clause about having everything.
qu'on
qu'on introduces the clause meaning that we have, after Est-ce. It is the contracted form of que before on, and it is used before the verb a in this question.
a
a means have here in the question about having everything. It is the form of avoir used with on; avoir followed by an object is a common way to express possession.
tout
tout means everything in this dialogue and is the object of a. It can be used after a possession verb to refer to all the needed things as one whole.
avant
avant places one action earlier than another; here it means before leaving. With de and an infinitive, it introduces an action that has not happened yet in relation to the first action.
de
de links avant to the infinitive partir, giving the meaning before leaving. The reusable construction here is avant de followed by an infinitive.
partir
partir means to leave or depart and is used as the infinitive after de. The citation form is already partir, and it follows avant de when describing an action that happens later.
Vérifions
Vérifions means let’s check and invites the two people to check together. It is the joint-action form of vérifier, used as a suggestion or instruction to begin an activity together.
maintenant
maintenant means now and tells the listener that the checking should happen at this moment. It is a time adverb that can be placed with the verb to specify when an action occurs.
Tu
Tu means you when speaking to one person informally. It is the subject placed before as in the question about the keys, and it is used with the informal singular forms of verbs.
as
as means have in the question about whether the listener has the keys. It is the form of avoir used with tu and is followed here by the object tes clés.
tes
tes means your before the plural noun clés. It is a possessive determiner placed before a plural possessed item, and it identifies the keys as belonging to the person addressed.
clés
clés means keys and refers to the items being checked before leaving. Its plural form follows tes and functions as the object of as.
Elles
Elles means they and refers back to the feminine plural keys. It is used as the subject before sont when giving the keys’ location.
sont
sont means are in the statement about where the keys are. It is the form of être used with elles, and it combines with a location phrase such as dans ma poche.
dans
dans means in and introduces the place containing the keys. It is followed here by ma poche, and this preposition commonly comes before a place or container.
ma
ma means my before the feminine singular noun poche. It is a possessive determiner placed before the noun and agrees with the possessed noun’s form.
poche
poche means pocket and identifies the place where the keys are. It follows ma in the location phrase and names the container or place introduced by dans.
Ton
Ton means your before the masculine singular noun portefeuille. It is a possessive determiner used before the noun being identified as belonging to the person addressed.
portefeuille
portefeuille means wallet and is the item whose location is being checked. It follows Ton and is the subject of the question with est.
est
est means is in the question about the wallet’s location. It is the form of être used with the singular subject portefeuille and is followed by a location phrase.
sac
sac means bag and identifies the container being asked about. It follows ton inside the location phrase introduced by dans.
Je
Je means I and is the subject of the reply about putting the wallet inside. It comes before the verb phrase and identifies the person who performed the action.
l'ai
l'ai refers to it and have together in the completed-action expression meaning I put it. l' is the object pronoun for the wallet, and it comes before ai, the form of avoir used with Je.
mis
mis means put in the completed action of putting the wallet in the bag. It is the past participle of mettre used with ai, and the object pronoun comes before this auxiliary construction.
dedans
dedans means inside or in there and points back to the bag already mentioned. It comes after mis to indicate where the wallet was put without repeating the container.
La
La means the before the feminine singular noun porte. It is the definite article placed before the door being checked.
porte
porte means door and is the subject of the question about whether it is locked. It follows La and is described by fermée à clé.
fermée
fermée means closed, and with à clé in this dialogue it describes the door as locked. It is the feminine singular form agreeing with porte and appears after est.
à
à contributes the meaning with a key in the expression describing the door as locked. Here it belongs with clé rather than functioning as an independent translation, and the expression specifies the way the door is locked.
clé
clé means key in the expression fermée à clé, which describes a door locked with a key. It is used after à to specify the key-based locking of the door.
vérifiée
vérifiée means checked in the reply about the door. It is the feminine singular past participle of vérifier, agreeing with the door referred to by l', and it is used with ai for a completed action.
à l'instant
à l'instant means just now and says that the checking happened moments ago. à links the time expression, while l'instant refers to the immediate moment; together they modify vérifiée to give the time of the action.