A restaurant, or an eatery, is a business which prepares and serves food and drinks to customers in exchange for money. Meals are generally served and eaten on the premises, but many restaurants also offer take-out and food delivery services.
If your employer has allowed you to keep the tips, you are allowed then to keep it. It is not a Sadaqa.
If one knows that a product is fried with non-halal meat, then it would become najis (impure) and haram to eat. If one didn't know then there is no sin upon them.
May Allah grant you success
It is not allowed to sit on a table having alcohol, but if you sit on a table which has no alcohol on it, it is allowed provided that you sitting in such place will not encourage others to be customers and drink alcohol.
Non Muslim seller who claims that the meat he is selling or wants to sell is Halal can not be taken as an authentic evidence that the meat is really Halal. If Muslim tells you that his meat is Halal and you have no reason to doubt his statement, then you can take the neat as Halal.
Restaurants selling alcohol or pork can never be trusted as utensils and plates used in cooking or serving alcohol or pork become Najis and and every other food put in Najis utensils and plates becomes Najis as well.
According to Ayt Sistani, there is no problem in having a Hindu server/waiter in itself providing you are not sure that he or she has touched the food with wetness.
The assumption in this case would be that they are not preparing the food hence not transferring wetness to the food- unless you have knowledge otherwise.
Furthermore, providing you have complete confidence that the food is halal both in terms of meat and the absence of cross contamination of haram/impermissible ingredients - ie alcohol, haram meat, etc. there is no Islamic legal requirement to inquire about the religious identity of the chef if you do not know his/her religion.
With all that said above, it is better to eat in trusted Muslim establishments where we are confident that the all the food products are halal.
If they close down with out any plans to restart alcohol business somewhere else, then helping them to sell stocks not linked with alcohol is allowed.
If they want to do the same unlawful business again, then it is not permissible to help them in any way.
In any case, helping in selling any material which can be used in alcohol is absolutely forbidden.
It is permissible to work as a dish-washer in a restaurant that could server alcohol, but regarding washing the utensils/cups that are used for alcohol, if doing such a thing is a preliminary for the serving/drinking of alcohol, then such a job would be haram. The income earned for such a thing would also be haram.
And Allah knows best.
In these mentioned cases, cross-contamination with najasah would make the food najis as well, and therefore haram to eat.
Unless you know that the common process in these restaurants is that they wash the pizza pan, change gloves, wash the knife, and so on. You can ask them these questions, and you can ask that the pizza not be cut, to avoid contamination from najasah.
As for using the same oven, that would not be a problem, because the pizza is put on a pan and then in the oven. If a pan is not used, then this is when there would be a problem.
In regards to french fries, or "chips", not only must the oil itself be halal, it must not have been used for cooking anything non-halal that is najis.
The oil must not be animal based, so it should be vegetable oil. What is cooked in it must not be najis, like meat that has not been Islamically slaughtered. However, if it is not halal to eat, but tahir, then there would not be a problem, like non-halal sea food. This is something you will experience in a fish and chips shop, where they might cook fish that does not have scales, or maybe even crab, in the same oil as the chips, or halal fish. In this case there is no problem, as long as there are no pieces of that food sticking to the food that you are going to eat.
And Allah knows best.
As jurists say, it is prohibited to buy or sell pig meat, but as for working in a place that serves pork, it is permissible. The problem would arise if you yourself were to prepare or serve the pork, in which case most jurists say it is of obligatory precaution to avoid.
You would need to refer to you Marja' Taqleed for the specific fatwa on this issue.
And Allah knows best.