For something really effective - probably just steroids, honestly (not recommended!).
I’m not below average and still young-ish, but definitely not built for strength either. Hitting the gym (a proper gym, with barbells and power racks for squats etc) helped a lot with girls, but only a little bit with gear.
Strong legs, strong core, grip are key. Use proper lifting form - don’t round your back, etc. My grip strength and lower back both suck, which is what limits me with gear. The bulky boxes, heavy tube amps, and big speakers all force awkward handling & weight distribution, on top of that. I could manage a 100 lbs dummbell in each hand for presses, but they’re all handle - could I ever manage a 200 lbs tube amp? Hell no!!
Gym should really be for your fitness goals, not for lifting gear. Get friends to help, or hire movers for the big stuff. It’s really not worth a back injury, trust me. Get youself a good set of Ironclad grip gloves - I don’t know how folks manage the slick cardboard boxes without those.