Use other add-ons
The CrashPanel core plugin, CrashCore, has everything you need to run various editors such as Script Editor, Model Editor, Particle Editor, and CrashPanel in general, but it has few implementations (only generic scripts and Custom Models spawned via command).
To get the most out of these editors, you need add-ons such as CrashItems, which allows you to create custom items (and much more).
Note that each add-on is a plugin that must be installed on your server.
In particular, these are the official add-ons:
CrashItems (download)
Items with custom textures and scripts, armor, GUI (with a simple GUI Editor), textured emotes, loot tables.
CrashItems, as you may have noticed, not only contains custom items but also everything related to resource packs (apart from Custom Models, which are native, and blocks).
CrashCommand (download)
For creating completely custom commands with Script Editor.
CrashBlock (download)
Custom blocks (with Model Editor and Script Editor support) and script-based world generation.
CrashMob (download)
Still very much a work in progress, it allows you to create mobs with custom models and behavior.
CrashAdmin (download)
Adds a real-time updated map and live panels to manage and control players (often used to play pranks).
CrashInvSee (download)
Adds a module dedicated to your inventory to the player page and its live panel (the one added by CrashAdmin), which you can edit in real time.