I have started writing down a few things here and there for my fiance in regards to pokemon games. She only got into Pokemon a few months ago, so she is still learning about types and items, etc. This is a little breakdown I made for her for buying items and how many to keep in her Bag while on her journey, if anybody would like to add to this feel free.

Healing Items

Potion Cost per 20hp 300
Super Potion Cost per 20hp 280
Hyper Potion Cost per 20hp 120
Fresh Water Cost per 20hp 80
Soda Pop Cost per 20hp 100
Lemonade Cost per 20hp 87.5
MooMoo Milk Cost per 20hp 100

Fresh Waters are best buy for healing between battles. Overall cheapest and restores 50hp. Two fresh waters cost 400 and a MooMoo Milk costs 500. So restoring with 2 waters is cheaper than 1 MooMoo Milk.

You can stock up on Lemonades early in the game by finishing Pokestar Studio movies. Your "fans" gift you Lemonades, Berry Juice, Escape Ropes. You can also get Lava Cookies from the Lemonade guy, I'm not sure what triggers the cookies though. Berry Juices can be sold to the Maniac on Route 5 for 1500 each.

Repels

Repel Cost per Step 3.5
Super Repel Cost per Step 2.5
Max Repel Cost per Step 2.8

Super Repels are the most effecient buy, you pay .3 pokedollars more per step, and for only 50 steps more.

I know its Noob stuff but she is a noob

Hey, I've done things like this quite a few times and definitely find this handy for the less-math-inclined Pokémon players.

I would say that this one depends on the game she's playing. Usually you can buy items that have the same function as Full Heal (Full Heals are 600 Pokédollars each), but for a much cheaper price.

Lava Cookie- Can be bought for 200 Pokédollars. Lava Cookies are only available in the Hoenn, Kanto, and Sinnoh regions. In Hoenn, an old lady on Mt. Chimney will sell you as many cookies as you'd like. In Sinnoh (only in Pokémon Platinum), you can buy Lava Cookies in the Dept. Store B1 level in Veilstone City for 200 Pokédollars. Technically you can also get Old Gateau in the Sinnoh region that has the same function as Full Heal, but you only get 1 of those throughout the entire game. In Kanto (Firered/Leafgreen only), you can purchase Lava Cookies from a market on Two Island. (Note: Lava Cookies won't be immediately available once you go to Two Island- you need to do a lot of business with the market until they add more purchasable items to their inventory)

Casteliacone- Can be bought for 100 Pokédollars, but you are limited as to the quantity you can purchase per day. This item is exclusive to Black, White, Black 2, and White 2 only. In Black and White, you can only buy 1 cone per day and they aren't sold at all when the season is Winter. In Black 2 and White 2 however, you're given the option to buy 1 cone or a dozen cones per day. Buying a dozen per day is definitely more preferable. (I also think Casteliacones can be sold in the Winter in Black 2 and White 2). In addition for buying the cones for 100 Pokédollars each, they can also be sold for 2000 Pokédollars each to a lady in the RV in Route 5. Selling them this way is definitely a quick way to make money because of the profit.

Games that do not apply to this: Pokémon Red, Blue, and Green, Pokémon Gold, Silver, Crystal, Heartgold, and Soulsilver, and Pokémon Diamond and Pearl.

One tip for easily training pokemon:
Step 1: Walk about and look for rustling grass.
Step 2:Walk into the grass
Step 3: DON'T FIGHT!
Step 4: Switch out to another pokemon.
Hope this helps you level up you pokemon a bit easier. Helpful if have no Rare candies!