[snip why it shouldn't have normal container functionality]

The bag of tricks is a great idea for further embellishment.

One idea: "previous result"
66% of the time the bag does what it did the previous time
it was applied.  34% of the time it 'rerolls' to have a new
result (rerolling until it picks something actually new).

Have this probability be more complex?
* Fireproofing ('fixing') the bag swings it strongly to previous.
* Depends on hero alignment (Law:70/30, Neu:50/50, Cha:30/70)

Possibly some effects do not happen again as previous results;
they force a new roll the next time the bag is applied.

Small chance that it damages/removes/destroys worn gloves,
and/or makes you drop wielded weapons and shields.

Should it scare you too?  Temporary paralysis a la ghosts.

BUC bag => BUC fire, right?

Would be cute if throwing the bag after this result
could make a stink bomb.

Since I suggested paralysis above, I think this result could
also be that something *does* pull you into the bag.  Two results
(separate entries)

1. The bag 'turns into' a trapper which automatically swallows
the hero unless a dex-type save is made.  Either this destroys
the bag or it 'turns back into' a bag when it dies.

2. The bag level teleports the hero.  The bag stays behind.
Perhaps if cursed, more equipment than the bag stays
behind.

Well, you could consider some generally non-harmful behavior of
the bag of tricks when it is depleted that would make it not quite
as good as a sack but not so bad that no one would use it.

Examples:
* When applied with no charges, the BoT, if empty, picks
up everything on the floor into itself.  No message/result if
there is nothing on the floor.  If not empty, the BoT
disgorges its contents onto the floor.  This makes it both
more and less convenient than a sack, but generally less
useful.

Putting a wand of cancellation into it should turn it into
a normal sack.

Hm I think looting should draw from the same results as applying,
but with only the results that sort of imply reaching in.  Or,
alternatively, it does the slurping up inventory thing above,
but with what's on the floor when looted from the floor, and
with your inventory when applied while holding it.

Falling into it like falling down a hole would also be amusing
(the bag staying behind, as above).

What about B/U/C status?

Is the BoT going to have the right number of charges?  I think
generating monsters was a useful result, and so if after the change
it does useless things half the time, perhaps it should have
twice as many charges?

Just idea.  Good luck, have fun..