The Subspace Suitcase is the purse-like case Ramona carries everywhere she goes. It's circular, with a shoulder strap and a star in the middle. It bears a star like the Subspace Doorways. Its capacity is unknown as it shares the same relative terms as the concept of Subspace, therefore it can be assumed it can carry quite a bit. Ramona uses this shoulder-bag to deliver the packages for her job and is rarely seen without it. Things that have been inside it at some point include: the package Scott orders from Amazon.ca to meet Ramona, the Large Hammer, the Titanium Baseball Bat, The Power of Love, and even Scott himself.
The concept of the Suitcase is likely based on a classic trope known as "Hammerspace", where a character from an animation or comic could pull out a large object from out of nowhere, or from a small storage place, or possibly as an homage to the Bag of Holding from Dungeons & Dragons.
During the final battle in Scott Pilgrim's Finest Hour, the suitcase is destroyed when Ramona uses it to block an attack from Gideon. When the case is destroyed, it explodes causing its contents to cover Chaos Theatre, and disarming Gideon. After he was defeated, Ramona found her bag's destruction to be an excuse to get a new one.
Ramona's Subspace Suitcase is symbolic of the emotional baggage she carries with her at all times. When it is destroyed at the end of the series, Ramona's "baggage" is sprayed everywhere, symbolizing an emotional release as she realizes that her love for Scott is greater than the issues of her past, and her willingness to discard it to protect and be with Scott as much as he would do the same for her.
In vs. the World
Not much is said about the Subspace Suitcase in Scott Pilgrim vs. the World. Ramona is seen wearing it throughout the film, and pulls her hammer out of it once, however, it received no further use.
In the Game
The Subspace Suitcase appears in Scott Pilgrim vs. the World: The Game. It is used by Ramona in her special attack. Ramona can also take usable objects out of the suitcase at the cost of some Guts Points. She also climbs into it upon completion of a level after doing her victory dance.