You have a number of untradeables, each with it's own respective benefits!
Ofcourse, these are not all of the untradeables but these are commonly used ones and allow me to cover most if not all information.
* Green highlight means it's applicable to each of the four best-in-slot untradeables.
First, let's discuss the best-in-slot and tradeable untradeables.
Infernal Cape : You will keep this untradeable at all times, however it does require a repair cost of 10.000.000 GP once it becomes a broken untradeable which happens when a Player dies with it at level 20 wilderness or higher, it can be obtained in a number of ways such as Vote Shop, Donator Store, Central Boss, HP event, Player Purchased or if luck is in your favor from Wilderness Caskets and/or regular and ultra Mystery Boxes.
Ferocious Gloves : it can be obtained from the Alchemical Hydra, Donator Store, Theatre of Blood.
Avernic Defender : it can be obtained from Theatre of Blood.
Ava's Assembler : it can be obtained from Vorkath and the Central Boss.
Common Untradeables.
Imbued God Cape(s) : You will keep the Imbued God Cape as an auto-kept untradeable below 20 wilderness but above 20 wilderness the Imbued God Cape will revert to a normal God Cape and the ether will be lost upon death, can be obtained here (requires a normal God Cape and x500 Revenant Ether).
Imbued Ring(s) : You will keep the Imbued Ring(s) as auto-kept untradeable(s) below 20 wilderness but above 20 wilderness these are lost! these can be obtained here for a cost of 25.000.000 GP for each Ring.
Abyssal Tentacle : You can obtain these by attaching a Kraken Tentacle to the Abyssal Whip which will turn it into an auto-kept item for 10.000 hits, after all 10.000 hits have been used the Abyssal Tentacle will revert into a Kraken Tentacle so be sure to check every so often or it might put you in a tough spot, like other untradeables the Abyssal Tentacle is penalized above 20 wilderness; instead of breaking it will be lost entirely if any other item protects over it!
Void & Elite Void : You'll keep these without risk of them being broken below 20 wilderness, above 20 wilderness these will break with repair costs ranging between 50.000 to 150.000 GP, these can be obtained in Vannaka's Untradeable Store!
Rune Pouch & Royal Seed Pod : You can use these freely at any wilderness level, these do not break and cannot be lost, the Rune Pouch can be found in Vannaka's Untradeable Store whereas the Royal Seed Pod can be found in the Vote Store a category also accesible through Vannaka.
I hope this helped, the reason I made this is to be more informative as quite a few new users still don't fully utilize their untradeables due to lack of information.
Sincerely, Wheelchairz.