Most flight planning systems don’t take airport environments such as congestion, expected runway for departure, CTOTs, unexpected weather, or other for fortuitous events when one shows up to the desk to pick up their paperwork. Manual adjustments on the EXTRA line, which are stabs in the dark at best, are required. One airport that comes to mind is LEPA. You can be number 14 for takeoff and if min fuel were taken you have just burnt your taxi and a good portion of your contingency fuel. There are other vacation destinations that have the same problem as well as arrival delays that are not factored into the flight plan.
A number of carriers use flight planning systems that run all of flight plans early in the morning at about 05:30(Z) the day of the flight(s) without updates.
Flights occurring 12 hours after the run usually results in forecast winds, temperatures, and weather different to which was used to run the flight plans earlier in the day. Some systems may be sophisticated to alert the crew that weather data used is outdated, if the flight is plan is greater than 6 hours old. I guess you can call ops and ask them to run you a current flight plan… good luck with that.
The load sheets of today are SWAGs at best. Estimated TOW is better than using the term SWAG on the flight plan. During cruise on full flights returning from vacation spots with 185 adults, and carry-ons, along with 220 bags in the holds, take out your performance manuals and work your way back to calculate your actual weight is versus the flight plan weight. I am always very happy to assume an almost MZFW versus flight plan weight. 2 tons can make a difference of 2,000 in cruise altitude resulting in extra fuel burn too.
Again, no airline is unique to this problem. There are times you just have to look beyond the flight plan and rely on experience and common sense.