I would have to say that I wouldn't advocate dealing in either art or stamps unless you really know what you are doing. And I'd especially not use it to try and avoid declaring savings, you may well lose more than you would gain.
Having said all of the above, paying off debt with your savings is fine for benefits, so make sure you are debt free (or as close as you can be) before doing so, as you won't be allowed to offset debt vs savings. Also, if you have any large purchases you need to make (a car, or a bike), go ahead and do it, as long as you can show some evidence that you did it for $ReasonThatIsntToAllowYouToClaimBenefits. If you've done it just to decrease your capital to allow you to claim, then it can still be counted as capital. If you've done it for $OtherReasonableReason then that's OK.
Don't take the above as absolute advice, it's been a good while since I was dabbling in benefits, and things may have moved on more than I think.