Kaunas is the second biggest city in Lithuania. It is quite a good place for dumpster diving but you need to know where the right places are and then you can definitely find some food or other useful stuff.
Mostly three supermarket chains, RIMI, IKI and MAXIMA tend to throw away food that is still in good quality. Other supermarkets usually sell "bad looking" fruits and vegetables or products with near expiration date at a discount. Most of the time, there is no practice to sort the trash, so everything is thrown into one large trash bin; sometimes, one can find bin-bags left near the supermarket skips that are full of exclusively bread, dairy, cheese, etc.
To get the best results, you could visit: 3 "IKI Express" shops in the centre: by the fountain in Laisvės al., by the municipality in Laisvės al., by the underground crossing in Vilniaus g. Closing time: 11PM, mostly fruit, bread, dairy. (Checked in Aug 2016, found bread, fruits&veggies at first 2 mentioned stores, some part of dumpsters were locked at the eastern iki express, so no luck there, but it still may be a good spot)
"Akropolis" mall right in the centre, trash is located in the closest passage northwest of the mall. The bins are sometimes guarded by security or annoyed employees, but they would not call the police. Mostly fruit and vegetable. Be sure to check smaller bins on the platform, not only the bigger ones on the ground – the former are where the goods are at. Check "Maxima" at the crossing of Daukanto/Kęstučio g., and other big "Maxima" shops in residential areas too.
"Rimi" in Šilainiai, by Apuolės bus stop (busses 3, 10, 37): recently opened, provides proper skip, but the fence keeps getting higher. So only good for good climbers.
Some examples of dumpster dived food in Kaunas:
Special dumping grounds ("Stambiagabaričių atliekų aikštelė" in Lithuanian) are another good place to find furniture, electric devices, wood, large pieces of glass, etc. There are two of them in Kaunas: Ašigalio g. 20 and Julijanavos g. 1a (more information in Lithuanian). Dumping grounds are fenced and have guards. Taking things from there is against the law but it is possible to do that after talking with a guard.
Freecycle group in Kaunas has 112 members and averages 2 messages a month as of May 2012. The communication language is Lithuanian but English is also accepted. Reach it here: http://groups.yahoo.com/group/kaunasfreecycle/ Check out the fb group "Freecycle/ Freegan/ Trash Notice LT", quite a few people from Kaunas sharing stuff and advice.