The rules state no weapons, but in reality it just means anything that can explicitly kill an opponent outright, such as ray guns or whatever. If it is part of a fighter's natural ability/fighting getup, then it's allowed (because everyone has that right). The rules also state no explict healing items, like Senzu beans
^The rules do not forbid anything else, as far as items. So, all four you listed are loopholes, not rule-breakers - Roshi's jar is an accessory that does nothing by itself; Potara Earrings are an accessory with a function that is neither a weapon nor explict healing; Paparoni's cane is part of his natural ensemble, it seems, and it's only functions seem to be the control aspect, plus 'maybe the robotic-esque fusion move he used; the 'love sticks' seem to part of U2's ensemble moves as well, as they commonly try to power each other up. For reference on that last one, Zeno punished Frost for attemptting to 'attack' another contestest from outside, and Shin warned Krillin against returning to help anyone; any direct, physical intervention is clearly against the rules, but indirect (such as the love sticks, or the Spirit Bomb) is not