Allen Wrenches...This day and age many things on guns use Allen Wrenches...One time I went out of town and my battery burned out on my Holosight.. Nope did not have Allen Wrench with me to change it out. I had the spare batteries but no wrench.. I have wrenches now...
Hand held manual Rivet gun and multiple packs of rivets. I found an outstanding autolight that works with a 12 volt battery...I installed that light..Now a head light on an old Nitelite soft cap...Light cost me $5.29. Now I have an additional head light to use..Like the light so much I went back and purchased two more...I drilled a hole in the Nitelite plastic light base and one in the auto light.. Used the right size rivet. Now I have an extra head light that works with 12 volt portable batteries I have.
Velcro...adhesive backing... different size.. Sky's the limit that you can attach things to your person, guns, lights with Velcro..Adhesive backing sticks anywhere too. Also assorted sizes of plastic wire ties... Same as the Velcro.. most times I use both so it makes the attachment real solid.
Scope Batteries spares and a screw driver that you can use to replace burned out batteries back at your car.. Notice I said back at your car...Probably while you have your head in the trunk too...Changing caps in the Field usually results in one saying "Oh!! _______now where did that go too?
Light bulbs for all your lights..
A nice size tool box to keep all of this stuff in or a nylon or tool bag.
WHAT ELSE?