Speaking of the compulsory currency exchange - you could always deposit it at the DDR Staatsbank for the next visit. I know someone who accumulated a considerable amount of money in the DDR Staatsbank through his frequent work trips (weekly for many years to East Berlin from West Berlin - the company sold products from neutral Western countries to the DDR and beyond, with East Berlin being home of the negotiations), and it was considered 'lost' money by his employer. After economic union, he had saved up over 25,000 East German marks in the account, which were converted, some at 1:1 to the Deutschemark and the rest at 2:1. He ended up getting around 15,000 DEM, which was a decent amount of money in 1990. That was on top of all the other money that he was allocated for 'entertaining', a lot of which simply went unspent.
As he says today, those were very strange times. He remembers once crossing at Fredrichstrasse and being told to "come this way". He thought he was getting arrested for something, only for the commander of the checkpoint to ask him if he could bring him a certain type of perfume for his wife. It turned out that they had confiscated a bottle of perfume a few months earlier, and the commander of the border post had taken it for his wife. Now that it was finished, she wanted more, and the commander obviously knew my friend was making these trips weekly.
An interesting postscript is that he obtained his Stasi file a few years afterwards, and they knew absolutely everything about his life, even down to the way that his office looked. However, they also remarked that he was the definition of professionalism, and that despite detailed and lengthy observation, he had never represented a threat to the DDR. I asked him why, and he said that as a Swiss citizen, it wasn't his job to judge who was right and who was wrong, only that he was there to do his job: negotiate and sell Swiss products to Warsaw Pact countries.
