Difference between the survey measured willingness to pay and the real decision in the shop.

Defining the perceived values of sustainability attributes.

Sustainable packaging influence on margin.

Green labeling effect on margin.

You can choose the topics related to the reasons behind consumer motivation to select a specific product. A good idea can be to apply the consumer motivational conflict for selecting/rejecting a product/service. If you choose perception as a topic, perceptual process is a nice area which you can explore. The book of Consumer Behavior by Henry Assael is a very helpful one in relating Psychology and Consumers.

Assael, H. (1998). Consumer Behavior and Marketing Action, Cincinnati: South-Western College Publishing.

Several realted topics you can work upon like

1. Consumer decision problem (experimental study) or descriptive

2. Cognitve Influence on decision making

3. Conative Influence on decsion making

4. Model of attitude development

5. Model of Percepual Defence

Neuromarketing grew three fold from 2011 to 2016 and is expected to grow further in the next few years. You can see the following article to read about it:

https://www.linkedin.com/pulse/trends-neuromarketing-2017-carla-nagel/

http://www.nielsen.com/us/en/solutions/capabilities/consumer-neuroscience.html

Totally agree with the contributors above that psychology is at the foundation of consumer behavior.

Amongst the issues that organisations have, includes a) segmenting their markets and b) building brand loyalty programmes. i.e. you have to know what people DO, and why do they do it (needs and attitudes) and what criteria do they apply when making a buying decision

You could use theoretical models such as Maslow's Hierarchy and the Golden Circle as a starting point. This to establish the motivators and underlying forces for the Consumer Decision behaviour. See also the Wheel of Consumer Behaviour (see http://www.stephenzoeller.com/how-apple-consumer-behavior-marketing/ ) See also my book at Business and Marketing Models at http://www.businessexpertpress.com/product-category/marketing-strategy/

Your study could be to compare the underlying psychological factors which differentiate the target markets of two or three companies. Do a comparison of their marketing strategies based on the 7P's

Or you could design a loyalty programme to drive the growth of a particular company by tapping in to the needs / motivators and buying behaviour of its consumers. Here you would compare the alignment of the loyalty programme with the business objectives...does the structure / function of the programme appeal to the target market and drive the buying behaviour desired by that organisation?

I would like to suggest my book Economic Aspects of Omnipotence (Scirp, 2015). In it I expalin the ostentations (and also this point can be through brands) process as drived by omnipotence feeling felt in childhood (based on Margaret Mahler e Melanie Klein). You can see it in most part of it, in google books)