I am trying to get ready for an intense backpacking trip in January. l have a lot of time but lately I've been combining endurance and weight training. Since school just started that weight has come in the form of my backpack (biology books suck) which has been weighed to be about 50 pounds and endurance is in my bike. l try to bike to school. The thing is lately it is been hot and this little routine is killing me. l have to get off the bike almost every half mile just to freaking breathe, plus my back aches already. Every night I am sore and feeling drained. Is there a way to make this easier cuz right now it is hellish.

l would suggest climbing stairs in an air conditioned building - that is what l do to train for big climbs. You may not need a whole backpack of books and may want to take some out so you get more flights

Good Luck

Or if u belong to a gym get on a treadmill at low speed but high incline with weight on ur back.
Biking with a heavy rucksack is never going to be easy, u might want to try doing steeper stuff without a backpack, or keep going for longer without a backpack.
Stairs r a good one though, definitely feel the burn in ur thighs..

Also, make sure you've got a well-fitting rucksack with a supporting internal frame, & that you've got it packed correctly with weight evenly distributed all the way up, to try & stop ur back from aching so much.