Energy gel/bars for cycling...do they actually work?

in 2 weeks i am cycling from leeds to liverpool in one day along the canal which is 127 miles. we want to limit the weight we are carrying which but will need lots of food. water isn't a problem as there are plenty of places to fill up. i keep seeing these gel tubes and energy bars in the shops and wonder if they're actually any good or just another pointless expensive accessory for the 'all the gear...no idea' type of poser bikers!...you know, the type who do 20 miles an think they can do the giro italia! hee hee, thank you