[sceptic]

what is your most undispensable convention and why?

[cherdano]

1♠ showing 5 spades (both as opening, or as overcall). No better preempt has been invented yet.

[Free]

Any relay bid

For openings NV: Lorenzo two's! 2X = 0-7HCP, 4+cards X, Majors first style

[Gerben42]

RKC Blackwood - I have found it essential in staying out of bad slams when we happen to miss two key cards.

[Badmonster]

Gambling 3nt? Or unusual nt? But I couldn't say they're the most useful conventions. They don't come up with the frewquency of say stayman or negative doubles.

[Al_U_Card]

Forcing NT (2/1 GF).

As nebulous as it can (must) be, it transformed the naturalish sayc into a force to be reckoned with. Altho it confuses the heck out of both opps and pards at times, it provides so many solutions to difficult bidding and rebidding situations that its value is inestimable.

[hrothgar]

First step, artificial and forcing:

Takeout doubles, negative double, Stayman, that sort of thing...

[FrancesHinden]

Take-out doubles.

When we've played as a fill-in pair during a holiday weekend, we play
*14-17 1NT
Stayman
*Weak jump overcalls
Take-out doubles
4th suit forcing
Splinters
Bid of the opponents' suit usually artificial and forcing
2C strong and artificial with a 2D negative
Artificial 2NT response to strong natural 2-bids

* these aren't really conventions of course

[Sigi_BC84]

Apart from the obvious that have already been mentioned: Inverted Minors.
--Sigi

[MickyB]

Definitely takeout doubles, followed by artificial bids of the opponents suit and the 4th suit. Can't think of anything close to those two - I guess various fit-showing bids come up next, including Drury if playing strong NT and 4 card majors (which I much prefer in 3rd+4th).

[mikeh]

If I were condemned to play 'natural bridge': sort of like culbertson in 1933, and could add one convention, it would be stayman. It is not as 'sexy' as my current 'favourite': a multi 2♥ opening bid, but it is the most important: with takeout doubles second and negative doubles third.

[MickyB]

I consider takeout doubles to include negative doubles, snapdragon doubles, etc - they are all just names for a double showing that you wish to compete.

I'm not sure that stayman is that important. 2suit nat NF, 2NT/3suit nat forcing works pretty well.

[pclayton]

Is undispensible similar to indispensible? OK I checked it - it is

Well, if you put it in those terms, the best invention of the 20th century was a strong 2♣. Basic negative doubles and splinters (what ELSE you gonna use a double jump for) are a close 2nd.

[han]

I agree with take-out doubles, including negative doubles and such.

[joshs]

Serious 7N. Its so much better than scrambling 7N and slightly better than non-serious 7N, which gets xed more often.

[mike777]

My most recent favorite has many names:
"reverse flannery" "FLOP", "The Cosmic Convention"

I put Stayman up near the top of any list.

[Echognome]

My favourite conventions are:

Snapdragon Double
Spiral Scanning
Psycho Suction
Prism Signals

Because they have the coolest sounding names.

[bearmum]

I like Neg doubles RKCB Stayman Q bids --- most of the others I can and mostly DO do without (ESPECIALLY in casual partnerships)

[Limey_p]

I am not big on conventions ... I prefer to have agreements. And the nicest ones to have are the ones that are so darned expensive when you are lacking them. I think these are all mentioned above:

low-level doubles - takeout, negative, support & snapdragon & similar.
4th suit forcing, new minor forcing
cue bid of opps suit
slam bidding - key card, control bidding