To give every container a breaking strain, that is, a maximum weight of contents which it can bear – so that to put the lead pig into a paper bag invites disaster.

The following shows the kind of "realism" rules which could be introduced using weights. Not entirely realistic: we do not bother to rupture containers out of the player's sight.

"Lead Cuts Paper"
A weight is a kind of value. 10kg specifies a weight. Everything has a weight. A thing usually has weight 1kg.
A container has a weight called breaking strain. The breaking strain of a container is usually 50kg. Definition: A container is bursting if the total weight of things in it is greater than its breaking strain.
A lead pig, a feather, a silver coin and a paper bag are in a room called the Metallurgy Workshop. The paper bag is a container with breaking strain 2kg. The lead pig has weight 50kg.
Every turn when a container (called the sack) held by someone visible (called the chump) is bursting:
   say "[The sack] splits and breaks under the weight! [if the player is the chump]You discard[otherwise][The chump] discards[end if] its ruined remains, looking miserably down at [the list of things in the sack] on the floor.";
   now all of the things in the sack are in the location;
   now the sack is nowhere.
Test me with "get bag / get feather / put feather in bag / get pig / put pig in bag / look".
Test me with "get bag / get feather / put feather in bag / get pig / put pig in bag / look".
Metallurgy Workshop
You can see a lead pig, a feather, a silver coin and a paper bag (empty) here.

>(Testing.)

>[1] get bag
Taken.

>[2] get feather
Taken.

>[3] put feather in bag
You put the feather into the paper bag.

>[4] get pig
Taken.

>[5] put pig in bag
You put the lead pig into the paper bag.

The paper bag splits and breaks under the weight! You discard its ruined remains, looking miserably down at the lead pig and the feather on the floor.

>[6] look
Metallurgy Workshop
You can see a feather, a lead pig and a silver coin here.