Nemesis Destiny
Adventurer
Don't let PCs take extended rests whenever they please.
I make mine wait until they've had at least 4 meaningful encounters under their belt.
Speaking from experience, this works. I have begun experimenting with extended rests only happening when story-appropriate, such as when the characters are in a town or comfortable area and have at least a full day or two to catch their breath. Being in the wilderness and having to forage and avoid monsters, trekking over rough terrain - these things make an extended rest impossible.Don't allow extended rest. Perhaps the sea is churning all night, there is a constant storm, or the ship crew is rowdy, and won't let you get in a good night's sleep. Or if they are in a jungle, constant rain through the night, or the howling of wolves, or some major threat that forces them to move around constantly may prevent an extended rest. You could even reward a partial benefit if and where needed, like everyone recovers a healing surge or some such.
There are also those who run games, redefining the meaning of extended rest to be "a week's rest", or "in between adventure's rest." This allows you to have as many time as you want pass by between encounters, for it to make sense to your story. I haven't tried this approach, but it works for some.
And my preferred method... don't make one encounter daysEven if there is supposed to be combat, you can narrate through the party sailing through Sahuagin infested waters, and skirmishing several groups of them along the way without major losses. It gets the point across without meaningless dice rolling.
Now, I do still get players who say, "but, but, it's been 12 whole hours since our last one!" and to that I say, "too bad. I guess you shouldn't have gone nova last fight. You'll have to make do with your encounter powers this time."
I do also make characters "earn back" their daily attack powers by having to buy them back with healing surges. I also do not allow the automatic recovery of hit points. The only way to get them back is with surges, so if you go nova and run out of both daily powers and hit points, your character is going to need some serious time to recover. Choose wisely.
So far, for the most part, it's been working. Once players got used to the different pace, the nova-factor decreased, and the whining stopped. I can get away with lower-level creatures in fights, and I don't have to worry about being a master tactician to challenge the group.