Some people prefer rules that mirror real life dynamics.
Carrying weight is one of those dynamics.
What is a theoretical spectrum of weight management system solutions and mechanics?
Seven Game Mechanics for dealing with equipment weight
What are some of the ways that games have dealt with carrying weight of items? I place two of the games that I helped create - ABS12 and 5e x 5 - into this seven tiers of weight management list.
Many games don't even worry about item and gear weight. Theoretically, a character could carry a dragon. Bags and gear stack on characters almost supernaturally. I remember playing a computer RPG where I was carrying over 50 weapons at one time. This might be a RPG where the list goes on into the thousands.
2) Gamemaster decides (ABS12)
Many, maybe most games, leave the carrying weight to the role played experience. If in the game the player tries to lift the item, the game master might describe the item as being unable to be lifted. Even though there wasn't actually a weight assigned to the item, through role play the item has now the characteristic of being unable to be lifted at least by this character and at this moment. The game master that is telling the story is left to decide if that item would even be liftable if the characters continued to try employing different methods of lifting. Maybe a spell could lift it. ABS12 doesn't really keep track of equipement. Equipment currently is tied to the vague and fuzzy gear which the 'what's good for the story' is the key to deciding what the player has.
3) Limited #
One easy method is to limit the number of items, not really focusing on the weights of the pieces. In computer RPGs, this is similar to slots in a bag or backpack. On paper, this might be a list of 10 items. In Fate RPG, important possessions are treated as an Aspect, to which beginning characters have a limited number of Aspects - normally the character begins with one high concept and one trouble aspects. Their background normally is three aspects related to the other characters. Most likely, if they have an important possession, that would be an Extra and function like one aspect (or skill, stunt). Other possessions may be explained or limited by the high concept or trouble.
At closer scrutiny, someone seeking realism might come to the conclusion that the bags and backpacks shrink and grow due to different size items. These containers when scrutinized don't make realistic sense. They however aren't meant to model real life dynamics. They are just doing the job of limiting your resources that you can carry.
4) Strength based maximum limit and simple weight (5e x 5)
Closer to realism is where an attribute such as 'strength' determines how much weight can be carried. In 5e (and 5e x 5), the default rule for carrying weight only calculates the maximum amount. This formula is 15 times the Strength score. As long as the character is below that amount, they can do anything normally. Over that amount and they can't move.
5) Strength based Maximum limits, a few increasing penalties, and simple weight
The optional rules of 5e move on to the next detail of rules
At x5 Strength score the PC suffers -10 movement speed
At x10 Strength score the PC suffers -20 movement speed plus a disadvantage with STR, DEX, and CON ability, save, and attack rolls.
6) Strength and penalty charts
d20 3.5 gets a little chrunchier. It has two charts. One is to look up the strength carrying capacity limits. The second chart looks up the movement penalty according to the character's movement speed. These amounts are not exactly the same as the quick calculations found in the prior example. They are more specific and vary in amounts.
7) Multi factor weight limits and penalties
Beyond the last example, the weight management really becomes a game within the game itself. Very specific rules, limits, and penalties may affect the entire game or portions of the game. If I was playing Rolemaster by the rules, I would need to keep track of weight and the penalties that would result from encumbrance.