Every day this week I've gone to the hardware store for a bolt for a different project per day

I need to find an assortment of Grade 5 bolts that I can use for cobbling crap together.  You guys have any kits you like out there?

I was thinking of wandering around the the local fastener specific stores to see if they have any home-builder kits.

Amazon. Bolt assortments. 

https://www.boltdepot.com/Product-Details.aspx?product=7506

I have a few assortments sitting around, but I've found they are never exactly right (example: I need a 13mm head but the assortment has 12mm in that size, washers not being the same thickness, etc.)

These days, I just order everything from McMaster-Carr. Stuff shows up in a day and it's always exactly what I need. 

As long as you only need sae I'd hit tractor supply and raid the fasteners by weight. Every time i go to get one fastener i add in a handful of anothor reasonable size and length too. Slowly filling a filing cabinet with grade 8 hardware ready to go

I spent a lot of money years ago on a full selection and now whenever one of the bins runs low I buy a box and dump it in. I have every common size and never have to do the bolt hunt. Money hugely well spent.