As the players round out their characters, there will be the question of what weapons, armor, and equipment they will start with. This is an issue both for parties starting at Level 1, and for one-off or advanced short-duration adventures where characters will begin at a higher level.
If your story’s setting has unusual mechanics, now is the time to address them. This may include a level of technology in your setting outside of the conventional “fantasy Middle Ages”. So if you intend for your story to take place in a very low level of technological advancement (bone and stone weapons, no metal, rare to find magic items) or an advanced level of technology (advanced metallurgy, gunpowder, plentiful magic items), the players should be aware of what weapons or armor are available.
Same if there are rules in your campaign’s society that prohibit possession or use of certain weapons, or armours, magic items, necromancy items, or even equipment such as lock-picking tools, venoms, poisons, certain spell components, or other items eschewed by your setting at large.
You may start your players’ Level 1 characters with the amount of gold prescribed by their Class (or even the maximum amount, instead of dice rolls for it). If you have a good reason to start your characters with an enhanced kit, do so, but only if you recognize that any gifts or enhancements you bestow make the PC’s stronger relative to your story’s antagonists.
If the PC’s are starting at a level above 1, they will need gear to match their level. Page 199 of the Dungeon Master’s Guide (DMG) gives information about PC’s starting above Level 1. A handy table on p.135 shows approximate wealth by character level:
Most players will purchase wisely if granted a budget from this table; beware of players who burn their bank on one overpowered magic item. Not because it’s a detriment to their character (likely it will be, and it’ll come back to bite them), but because the item could cause problems in your game.
You may need to establish what magic items cannot be found in your campaign; particularly if teleportation, instant-kill, or especially undead-bane-y magic items will break your game. Generally as the DM you can simply not have any ‘dangerous’ items found in treasure-drops or from merchants. It’s when players are let loose in the DMG’s “Magic Items” section during character creation at higher-level starts that you have to reign in (likely by veto on inspection of their character sheet) what they intend to bring into your game.
With starting equipment, you should also establish how closely your campaign will adhere to rules concerning weight and carrying capacity, food and gear, and incidental expenses.
Some DM’s follow Tables 9-1 and 9-2 (Player’s Handbook, p.162) to the letter; insisting that players track their character’s encumbrance down to the pound and apply penalties to movement and DEX.
This attention to detail also extends to food and gear. You may want your players to account for all the food and water their character would need each day, and for your players to note the depletion of torches and consumables in their stash.
In terms of money, some DM’s want their players to keep close accounting of their platinum, gold, silver, electrum, copper, gems (whatever currency your realm uses) to make sure the characters are paying for drinks at the tavern, accommodations at the inn, stabling for horses, meals, spell components, repairs, fares aboard ships, and so forth.
If you want this level of attention paid to minor details is really up to you. It will depend on how focused your campaign will be on the little details. The players should know this up front so that they may cautiously purchase their starting equipment and save for future needs.