This is a container clue - look for indicators like 'around', 'holding', 'outside', 'embracing' where one part wraps around another
Break down the clue into definition and wordplay parts
Answer: PLASTICBAG | Definition: 'lightweight item' | Wordplay: BAG=”Thing” (e.g. ‘that’s not my bag’ = ‘that’s not my thing’); after PIC (picture, “film”) around LAST=”final”