May one use the oil that remains after the candles have extinguished?
The leftover oil of the 8th day’s Chanukah lighting is to be burnt on its own if it extinguished prior to burning for a half hour. [This same law applies for the leftover oils of any other night, although one may simply reuse this leftover oil for the lighting of the next night. This is with exception to the 8th night in which the leftover oil must be burned on its own due to it being the last night of Chanukah.] If the candle contains more than 30 minutes worth of oil, then the first thirty minutes of oil [lit past nightfall] is considered designated for the Mitzvah, while the oil that remains after these thirty minutes does not contain any Mitzvah status. [However other opinions rule that all the oil is designated for the Mitzvah and thus may not be used for any other purpose. According to all if one stipulated on his oil that only the oil which burns for the first half hour is designated for the Mitzvah, then the remaining oil may be used for other matters. Practically it is best to suspect for the latter opinion and stipulate upon placing in the oil that all oil that remains past a half hour is not sanctified for the Mitzvah.]
What should one do with the leftover wicks of the Menorah: The leftover wicks of the Menorah are likewise to be burnt.
After Chanukah, the leftover oils and wicks which were used to light the Chanukah candles must be burnt after Chanukah. It is forbidden to use them for any other purposes. It is proper to stipulate before Chanukah that the oil which remains after the 30 minutes of lighting is not considered designated for the Mitzvah.
 Michaber ibid as explained in M”B 677/18 that “Hatzarich Leshiur Hadlaka” means that there was enough oil to last 30 minutes and it extinguished before that time.
The reason: As the oil of the half hour of burning as designated for its Mitzvah. [Michaber ibid]
 M”B 677/17
 See Biur Halacha 671/1 “Ubilvad”
 Michaber ibid as explained in M”B 677/18
 Poskim brought in M”B 677/18; 672/7
 M”B 672/7 in name of M”A
 See Kaf Hachaim 677/26 in name of Levush