In any disaster or emergency, a bug-out bag is a key to survival. If your grandfather prepared a bug-out bag years ago and you never faced any emergency then it is sensible to upgrade the BOB.
You will find better survival kits in the industry and you shouldn't solely rely on what your grandfather purchased. The prime idea is to keep it powerful and prepared. You can buy couples and family survival bags whenever required.
There's nothing wrong with leaving the survival kit untouched for months and some things can be abandoned for ages.
However, if any edible items are left for quite a long time, they'll go rancid. When you bug out in a rush, there will not be any point in carrying heavy crap that you can not even use.
The parts of the Bug out bag must be kept clean, recharged, assessed, and replaced so the survival kit stays effective. As an example, you can set a check card that will reveal the expiry of the contents inside.
On the flip view, there are several long-term storage things like spotlights and radio receivers that may stay effective for ages.
But it is possible to drop in from time to time to confirm their effectiveness. The batteries must be kept unpacked and out of the apparatus where they need to be used.
In line with this sod's law, the batteries stored in the kit will flow dramatically if they're kept in a costly kit. So once you need to bug out, ensure that your kit can deliver what's expected from it.