! You've already received a pokémon and started your career as a pokémon trainer.
Wanting practice battles. Like all NPC trainers, they pay you money if you win. And if you lose, you die. So.
There is a building called House of the Berry Brewers, where several alchemists work to teach trainers how to find the right berries and plants and how to make potions and medicine from them. (healing items, status ailment items, repels and vitamins)
gives you an Old Rod if you do him a favor. "A favor" means it's up to your creativity.
gives you a PokéGear with a map, a radio (with headphones, yay!) and the possibility to contact important NPCs when you have their number, if you travel to Mr Pokémon on Route 30 and bring back an item that the oddball refused to send without personal escort. The item is (not surprising) a pokémon egg. Note: the mayor is a woman.
Fishing in sea with Old Rod:
If you did not speak with the mayor in Cherrygrove, Mr Pokémon will ask you to deliver a strange pokémon egg to her back in the city. The mayor will not give you any reward. If you return to Mr Pokémon afterwards, he will give you a Pokédex that he apparently had laying around. With the pokédex, you can easily keep track of what pokémon you have seen and captured, and read trivia and information about them and their abilities and habitats the the in-game menu wouldn't tell you. It can also sense if other pokédex holders are in the vicinity.
Fishing in ponds/rivers with Old Rod:
In the Dark Cave:
NOTE: you can't have done any of the quests before the start of the RP - except for New Bark Town and Route 29. If you want to start in Violet City (in case your character is likely to be at the front lines or something?) but still want a pokédex, you'll have to write about traveling back and doing the quest to get it.