Trunks
-Complete Dragon Universe mode with Vegeta)
Uub
-When fighting Kid Buu use the spirit ball technique as normal or kaioken and it will become the Super Spirit Bomb, just win the attack and there will be a continuation of DU)
Vegeta
-Defeat Vegeta in Dragon Universe mode with Goku.)
Videl
-Hercule's daughter can be unlocked only while in Gohan's DU. Before your battle with Dabura, search fields east of Goku's house for one event with Videl, then search the island chain in the lower right portion of the map. You should find a spot that will initiate a second conversation with Videl about how she's being trained, and afterwards, she will be unlocked)
SS4 Vegeta and Vegeta’s SS4 Gogeta Capsule:
In Vegeta's 2nd DU, as soon as Vegeta is resurrected after Fat Buu, go to muscle tower on the ice island. There you will automatically talk to kibitoshin about Broly. Then go fuse and fight Buu at the dot. As you go to fight kid Buu Goku will instead send you to find and kill Broly. Once you can move, instead of flying to Broly, fly around the chain of islands to the SE. Here you will see a event with Vegeta complaining about Goku while King Kai makes it so Goku can here Vegeta complain. After that go kill Broly. After Broly, Vegeta will sense a new power but it's not evil. instead of heading to the new dot to the south, go talk to piccolo at kami's tower, he will question him. After, go towards Baba’s palace. in a "plains" area you will talk to Bulma about Goku turning ss4. Then she tells you to go home (West City) for a surprise. She gives you the SS4 capsule. Now go beat Goku at the red dot to the south. If you beat SS4 Goku, you will get Vegeta’s capsule for SS4 Gogeta!
Kabitoshin
-To unlock this potara fusion, you must play though Gohan's (Adult) DU a second time. Follow the events to unlock Supreme Kai (as shown above) and then fight and defeat Kid Buu with Gohan. Once you do, do no head to Broly's red dot right away. Instead, go to Central City, and then fly
directly west to the coastline. You should find a small island covered in forest, where there is a 'forest' event. Activate the event, and you will get the Kabitoshin capsule.)
Cell Games
-Beat Cell in DA when he breaks in( Your character must be lvl 20-30 and fight lvl 52 Nappa)
Membership Cards
-Silver- Obtain in DU when you get a character above lvl 2 or spend 1,500 zenie in the skill shop, then you can buy it.
-Gold- Obtain in DU when you get a character above lvl 15 or spend 100,000 zenie in the skill shop, then you can buy it.
-Black- Obtain in DU when you get a character above lvl 30 or spend 250,000 zenie in the skill shop, then you can buy it.
Z Modes
-Z Mode- Complete DU as a character on very difficult mode.
-Z2 Mode- Complete DU as a character on Z Mode.
-Z3 Mode- Complete DU as a character on Z2 Mode.
An easy way to get these is to choose someone with a short DU like Uub and only fight the last character on the highest mode.
With thanks to Mark Miguel and Nick Valent at IGN for tips.