I had always been like that, so it is not dementia for me, and had been like that until I found a solution. Here it is:

I only buy bags/purses from this site best selling handbags and purses | baggallini(R) and by the way, it now has a 30% off everything sale. Their bags have wallets and attachments for keys tied to the purse, so that you cannot lose keys or a wallet. I keep my credit cards in a plastic case which I have had for close to 10 years and it appears indestructible. The case goes into the wallet that is attached to the purse. The keys are attached to the purse. The current purse is big enough for my laptop and has a special compartment for it. I also keep my sunglasses in a case in the purse. The sunglasses case is not attached but knock on wood I have not lost it. In the past I had one instance of losing very expensive sunglasses which were new and I did not find them. I figured that it happened because those sunglasses could not be worn as a headband. Since then I have only be using sunglasses which I can wear as a headband when it is not sunny outside or when I step inside. When they are on my head, I cannot lose them.

I have been using this system with Baggallini purses for more than 5 years and have never lost my keys or wallet during this period of time. It appears to be a foolproof system. It does not protect against putting your valuables into trash, but it does protect against losing small objects, because the purse itself is a large object which is hard to misplace.