Rules

I try my best to follow the rules as laid out in the 5e PHB but will sometimes get confused with Pathfinder rules but here are also some rules that I know are not in the rules, most are better for the players and some not so much but this is how my world works.

Two weapon fighting
If you use an attack action you can then use your BA to attack with a second weapon but you don't get your ability mod added to the BA attack unless its negative. Both weapons must be light unless you have the two weapon fighting feat.

Drinking potions
To drink a potion yourself it is a bonus action, while feeding one to another character is an action.

Death
To make death a more serious there is a chance that even a resurrection spell is cast on you it may still not work, when a spell is cast the GM will roll a resurrection check DC10, the DC increases by 2 for every previous resurrection, the DC can also be modified by up to three skill checks if there is time for them to be performed, the final factor is how badly the dead persons wants to be revived which will modify the DC by up to 3 in either direction depending the strength of the argument for or against returning.

Movement
The first diagonal movement made in a turn costs 5ft of movement and the second costs 10ft the third is 5ftand fourth 10ft and so on for however many diagonals you move in a turn.

Donning Armour
To don or doff armour, there are three stages, each with different effects. It can take a different amount of time to progress through these stages based on the type of armour. The first stage is gathering/preparing the armour; this can be as simple as picking up all the various parts or it may consist of putting on the layers of cloth and padding required for the armour. During this stage, you have no advantage or disadvantage from the armour yet. Stage two is actually putting the armour on your body which, until it is properly fastened, provides less defence than normal, but still induces the same penalties. After this stage, the armour provides half plus five of its original AC. The final stage is fastening the armour. During this stage, you can't move more than 10ft during the same turn that you make progress on donning your armour. Armour is considered fully donned after completing Stage 3. Other characters may spend their Standard Actions (SA) or Bonus Actions (BA) to help equip the armour, so with enough people, armour can be donned in 1 turn. After Stage 1 = nothing, After Stage 2 = Dex modifier and Stealth disadvantage if appropriate + reduced AC,   After Stage 3 = Armour donned.

Sleeping in Armour
You can sleep in light armour but its less comfortable and you wouldn't do it in a place you felt safe. You can sleep in medium armour but only regain half of your missing Hp and 1 spell slot of each level you then must make a constitution saving throw DC10 or receive a point of exhaustion. You can't sleep in Heavy armour, you may wear your under armour padding which will save you 1BA and 1SA in the donning process.

Travel
When traveling cross country there are a number of factors to consider, such as the type of transportation you're using, the amount you're carrying, and the haste with which you're moving. The amount of time you spend traveling in a normal day is 10 hours, including an hour and a half spent taking breaks of various lengths, such as stopped for lunch or resting. Also, the drain of traveling causes you to lose efficiency if you travel for too long with out stopping. Every 5 full hours spent traveling causes a loss of 30 minutes of travel.

This table shows the speed you travel per hour / per day in miles


 * such as Swamp, Mountains, Forest

Mounted Combat
Mounting and dis mounting as well as falling from a mount is as seen in the PHB pg.198. If your mount is intelligent it may act on its initiative if not on your turn you may use your movement to make your mount carry out a dash action, then all none intelligent mounts move again at Initiative 0,

While mounted Melee attacks receive +1 to dmg for every 10ft of movement in a straight line prior to the attack but suffer -1 to the roll to hit.

While mounted unless you remain stationary for your turn you need to roll an Animal Handling check before attacking with a ranged weapon, DC 15 or receive a -1 to your attack roll if you fail by more than 5 then you receive -3, unless your trained in mounted archery when no animal handling check is required.

While mounted unless you remain stationary for your turn, to cast a spell you must succeed at a concentration save DC equals 8 + the spell level. or the spell fails and you must make a DC 10 concentration check at the start of each turn to maintain concentration of a spell.

Stowing and drawing weapons
During your turn, you may stow or draw items twice for free. This means you could stow one weapon and draw a second, or draw one weapon and one shield. It also means that if you are using a bow on your turn and then get to make an attack of opportunity, you may only use an unarmed strike, or your bow as an improvised weapon, not stow your bow and draw a sword.