Maybe Dr. No didn't want to give them time to plan an escape.

I figured the drugged coffee was just to portray Dr. No as a control freak, a power maniac, a bad guy.

Not quite. The idea was put anyone who came near Crab Key through this assault course as a test of endurance. Each one would start equally fed and rested to obtain accurate results.

That was pretty thoughtful of Dr.No to do that for Bond. Doesn't seem that bad of a villain.

Wow, very interesting Tony. Thanks for the insight

It's another one of those things that are in the book but get lost in the film, like Goldfinger explaining his plan in great detail and then gassing everyone.
In the book the escape route through the pipes is an assault course ending with Bond in an enclosed bay with a giant octopus. He's the first to run this gauntlet. Dr. No drugs the coffee to make sure he gets proper sleep and is properly rested to face this ordeal

haha ok, glad other people agree with me. It always bugged me

Bond is showning us his suave survival skills and coolness in the face of adversity.
("How can you eat at a time like this?" "I'm hungry, who knows when we'll get to eat again! - psst, the place is bugged.")
But what next? "Mmm, that hit the spot, well I'm off for a kip, g'night."
That won't do, but he can't bang Honeychile 'til the end of the movie. He hasn't been in any real danger for at least 7 minutes, soo
As Honey nods off, Bond tastes coffee again.
DAMN! .. (shakes head) .. THE COFFEE . . (smashes cup!) -
(blinks determinedly) . .
(stuggles to his feet) . .COFFEE WAS . . DRUGGED! -
( steps forward, leans heavily on tray) . .
. .
( unsteady; eyes roll . . Crashes to floor!!) -
(unconscious on floor)
(floor level: legs and feet enter, begin to drag bodies ) -
( guitar chord ) . . .
Fade to Black
And, viola, Bond is, once again, in apparent danger. O, the suspense!!
Sadly, the scene is played with all the finesse of Captain James T. Kirk.
Your right, OP, it does nothing to move the plot and makes no sense.
You Fill Me with Inertia.

From the Trivia Section:
"Peter R. Huntused an innovative editing technique, with extensive use of quick cuts, and employing fast motion and exaggerated sound effects on the action scenes. Hunt said his intention was to "move fast and push it along the whole time, while giving it a certain style", and added that
the fast pacing would help audiences not notice any writing problems.
"
There's so many continuity problems with this movie it should be a Drinking Game.
You Fill Me with Inertia.

I'm of the same opinion and actually came on to ask the same question. They'd already taken their clothes due to the radiation, so they had nothing to search. Perhaps there's a reason in the book. Another thing is that after drugging them, someone came in and put them to bed.

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Dunno, could be they wanted time to prepare the dinner before hand.
top 50 http://www.imdb.com/list/ls056413299/