Don't worry. Your FRBs will get heavier and heavier with practice. 10lbs is a very respectable weight
If you want to get more of your dollars worth out of your FRB, include batteries and/or handwarmers. Batteries should be in original packaging or, if included in an appliance or something, removed and wrapped in plastic so they can not make ground to anything, per USPS regs. Handwarmers, if not already in a second outer wrapper or box, I try to remember to put in a ziplock bag to reduce risk of the wrapper being torn.
My heaviest packages are generally canned goods or popcorn. I reinforce boxes with canned goods that are dropped by sling-load because someone (I forget who) reported a package of soups rupturing in transit last year. Arranging everything to fit without the box bulging is like fitting a puzzle and takes a few tries. My postal clerks WILL send me back home if the flaps don't meet or the box bulges noticeably. *Standard* hygiene or snack packages are usually 10 to 13 lbs, mostly depending on how many batteries I squeeze in. Packages that include special requests are usually lighter than that just because I'm working with unfamiliar shapes.