Some Basic Comparative & Superlative Adjectives
This is somewhat tricky for most Singaporeans.
Consider the following
Positive Comparative Superlative
A Less Lesser Least
B Little Less Least
Our example above should have been 'Use Less Bags' since the intention was to use the it as an adjective (A). It modifies Bags (How many bags? 1, 2, 3...Less).
'Lesser' only appears as a comparative adjectve (A) when you need to compare across two things such as 'lesser of the two evils', a common phrase.
In situation B when we are refering to something very little and few (POSITIVE), its comparative would be 'less/fewer'. E.g. We don't say 'You exercise less' unless it is a comparative 'You exercise less than [someone]' where the object is obliterated.
This is known as null-comparision.
For more discussion on 'less' and 'lesser', you can refer to http://englishplus.com/news/news0701.htm/
Most Singaporeans need more practice in the Engllish language, so that we make less of these mistakes and least of all, support the 'Speak Good English' campaign ( or 'write' for that matter).