Polish Native speakers: Should I attempt the correct endings or just use the nominative form?

I'll be in Poland trying out my Polish next month. I'm wondering if native speakers can tell me which would be better:

1. To attempt the correct declensions but get them wrong, or
2. If unsure to just say the word in nominative form?

Would a native speaker be able to understand what I was trying to communicate if I didn't put the right endings on my words? I will only be creating basic sentences, something like "Czy mogę mieć herbatę, proszę?" Does it make more sense to say "Czy mogę mieć herbata" or "Czy mogę mieć herbatu" (this is an example of a mistaken ending I might use.)

I'm trying to imagine it from my perspective: if a Pole attempting English were to ask me a question, would it be easier or harder for me to understand what they were trying to communicate if the words were in the correct order but missing the right prepositions, or if they had the correct prepositions but were in the wrong order? I think the second:

For example: "I am taking my dog to the park this afternoon." "I take this afternoon my dog to the park" is understandable if clumsy, but "I take dog to park afternoon" isn't as clear.

Thoughts, anyone?

Try the endings.

Well, first of all not everything can be translated directly from English to Polish. E.g. We don't say Can I have a tea please - we do not say "czy mogę miec". We just simply ask - poproszę herbatę.

I think that as long as you will more less pronounce words correcty, people still will be able to understand, even if you get the grammer wrong.

Have fun :)

You would probably learn more if you attempted the correct ending instead of just saying something you already know is incorrect so if I were you, I would try to say the word with the right ending and practice, practice, practice.

Incidently, the form "czy mogę mieć..." is not Polish; it is a Briticism, it is acceptable, but this is not how the natives speak.

Instead:
"Proszę (poproszę) szklankę herbaty"
"Czy może mi Pan/Pani podać kubek herbaty?"
"Czy można prosić o filiżankę herbaty?"
"Czy mogę prosić o herbatę"

Google suggest that Poles still prefer "szklanka herbaty" (50%) than "kubek herbaty" (30%) and after that "filiżanka herbaty" (20%).

Kubek is Anglo-muggy and crude. Tea should be drunk out of a teacup or (the eastern way) glass with holder, and, coffee out of a demitasse. Mugs are good as a kitchen utensil when cooking or in the bathroom when lathering up shaving soap with a brush, but not much more. Just because you seem mugs in offices in Hollywood films doesn't make them 'cool'.

Pol3, you are so out of your time, you have no idea of what PL is about.

I would prefer the second, the word in nominative form
but if you feel confident try endings.

We don't use a lot of run up words such Can I have a ... please.
We can be polite or ask just by using a proper tone.

Eastern way? You mean...communist way.

In my opinion it would be better to use the correct endings as it will be easier for the listener will pick up on what you are trying to say but the only thing is that this will take a lot of work to get right.

Thanks for all the feedback! I made up that sentence about the herbata because that's the level of speech that's going to come out of my mouth when I try! I'm finding that I don't know enough polish verbs... I just don't want to end up being even less comprehensible if I use the wrong endings-- I don't want to think I'm communicating one thing, but I'm actually being more confusing because I'm using the wrong case.

just say...
daime herbata
why make things complicated..;)