Robin Walker has stated that at one point that Valve team members would refer to Sticky Bombs as "winbombs", due to being perceived as too powerful by the team:

Within the game's files are unused models for a red version of the robots seen in Mann vs. Machine (except for the tank and sentry buster), which can mostly only be seen by modifying the game's files. However, the red model for the robot Spy is used when a spy disguises itself. This could imply that players were originally going to be given the choice as to which team they would play as in Mann vs. Machines matches.

One of Spy's lines when talking about the Conga taunt, "Dancing! It is the forbidden dance!" is in reference to the conga being a dance that originated in Cuba, and was forbidden due to people believing it induced excitement and adrenaline, and was blamed for causing fighting in the streets near elections. Cuban president Fulgencio Batista permitted the people of Cuba the right to dance the conga, but only with a police permit.

There is an unused texture for the RED Medic's head, which features a lighter and shorter hairstyle, which was previously seen in one of the game's trailers. It is listed as medic_head_red in the game's files.

The Soldier Costume Transmogrifier, added in the Halloween update of 2013, had a bucket included in its backpack icon, which all other class Transmogrifiers lacked. This was an early reference to the Team Foretress 2 short animation, "Expiration Date", released in June of 2014, and the Soldier's obsession with a similar looking bucket in the animation.

There are several unused voicelines that were added during the Love & War update that suggest a feature where the classes make fun of another player's weapon or hat, as well as a number of lines related to trading.

There are unused particle effects with names that relate to the "Conga" taunt. This suggests that the taunt was originally intended to constantly spawn confetti, streamers and fireworks, which are either green or pink.

The sniper rifle "The Classic" is a remake of the sniper rifle found in Team Fortress Classic.

When the 'Meet the Spy' video was released, The Sniper playermodel was updated in the game, adding the scar that the sniper got in the video. Previously, he had no scar on his face. It was never taken off the player model, and still has the scar.

The Stickybomb Launcher bears resemblance to a weapon cut from Half-Life 2, simply named the "Sticky Launcher". Had it been included, it would have functioned in an almost identical manner, except that it would stick to enemies as well as map surfaces. Also, the Stickbomb Launcher was originally supposed to be the Pipebomb Launcher seen in Team Fortress Classic, but it was changed to the Stickybomb Launcher as the Pipebomb Launcher's only difference was that you could detonate the pipebombs with the alt fire key. The model remains in the game.

One of the Scout's taunt attacks, called the Home Run, is a reference to Babe Ruth's famous "Called Shot" where he points to the sky, and hits a home run. The scout repeats this, and proceeds to bat any enemy caught in the swing 25 meters away as stated in the related achievement "Out of the Park".

The weapon Cleaner's Carbine, and the hat Liquidator's Lid both reference the hitman from the French film "Léon: The Professional", who refers to himself as a "cleaner", rather than a hitman. This view of himself also reflects that of the Sniper's, as he always refers to himself as a "Professional" rather than a psychopathic killer everyone sees him as. The description of the Liquidator's lid also alludes to the lead guitarist (The Edge) of the Irish rock band U2, who wears a similar tuque.

During the Love & War update, using a Teleporter can cause a random piece of bread to spawn at the exit. This is a reference to the video "Expiration Date". The chance for bread to spawn from the Teleporter is 1/20, with a hardcoded exception for the Soldier where the chance is a much higher 1/3.

Ludmila is a scrapped unlockable primary weapon for the Heavy. Its appearance was later used for Natascha, and the model is still referred to internally as "c_ludmila".

The P.D.Q. was a scrapped melee weapon for the Engineer that was tested in the Team Fortress 2 Closed Beta. It used the game's Wrench model.
The P.D.Q. does not have the ability to be used to upgrade buildings, and instead increases the Engineer's rate of construction by 150% when hitting the building with this weapon.

A Fire Retardant Suit was a scrapped secondary weapon for the Spy that was available for use in the Team Fortress 2 Closed Beta.
Two variants of the Fire Retardant Suit are known to have been tested. The first Fire Retardant Suit simply reduces incoming fire damage by 90%. The Fire Retardant Suit Beta 2 does not reduce fire damage, but instead grants the wearer complete immunity to the afterburn effect.

The Branding Iron is a scrapped melee weapon for the Pyro. It is an over sized branding iron which bears the initials 'TF' on its head.

The Pyro's "Coffin Kit" has a note on its side which lists the names of various regular item contributors from the TF2 Emporium's Steam group chat. The top name on the list, "Sexy Robot", is the creator of the "Coffin Kit" item.

Heavy's cosmetic item "War goggles" was based on the Heavy class from Team Fortress Classic.

The hat "Deep cover operator" for the Spy and the Sniper is a reference to "Snake" from the Metal Gear series. The hat was also contributed via the Steam Workshop under the name "Fox-Tie Wall Camo", a reference to Metal Gear's FOXDIE.